CN110799431B - Packaging method, flexible container, package and method for cooking food - Google Patents

Abstract

The present invention relates to a method of packaging thermoformed food products and to dual ovenable thermoformed food packages suitable for direct cooking of the food product in the package in microwave ovens, conventional ovens and convection ovens. These packages are characterized by good air tightness, clean peelability, self-venting, very good optical properties and, if shrunk, a very attractive appearance.

Description

Packaging method, flexible container, packaging and method for cooking food

technical field

The present invention relates to the use of oriented polyester films in thermoforming food packaging processes, in particular deep drawing and thermoforming-shrinking food packaging processes. Furthermore, the present invention relates to a dual bakeable thermoformable package, in particular a dual bakeable thermoformed food package for cooking with the package.

Background technique

Cook-in-package, i.e. packaging in which the food can be cooked directly in the package, in a microwave or conventional oven, in boiling water or steam, is becoming more popular as it reduces the time spent in meal prep , is effective, requires no cooking skills and allows for better portion control.

In addition, if cooking is done in a complete package, the cooking time is generally reduced, the oven is kept clean, no unpleasant odors are released, and the flavor of the product is preserved.

In certain applications, such as when cooking fresh fish products, packaged cooking methods are particularly desirable because they avoid handling raw fish and reduce the risk of contamination. Few plastic materials are suitable for the most demanding dual-bake packaged cooking applications, namely the following:

- Microwave transparent for cooking in the microwave (microwaveable),

- resistant to temperatures above 205°C and up to 220°C for high temperature cooking in conventional ovens (bakeable),

- able to seal tightly enough to prevent leakage from the package during storage and transport, but at the same time peel off easily for smooth opening, and self-vent to allow steam to escape from the package during cooking,

- Ability to provide food with a high enough core temperature to kill pathogens and bacteria throughout the cooking process,

- Transparent and non-whitening during cooking to allow inspection,

- Approved by regulatory agencies for food contact use, i.e. no release of contaminants throughout the processing cycle including any pre-cooking, packaging, heat sealing, storage and cooking steps.

The materials that have been mostly developed in practice and used for the manufacture of double bakeable packaging are mainly based on polyesters.

In the prior art literature, such as those disclosed in WO2007093495, WO2009013284 and WO2012160142 in the name of Cryovac or available on the market, double bakeable packages typically comprise a bisque oriented lid sealed with a flange around the tray. Heat-shrinkable polyester film enclosed plastic trays (packaging with lids for double bake trays).

Other dual bakeable packaging may include bags or pouches enclosing food products, wherein the bags or pouches are prefabricated according to conventional bag making methods or in-line from dual bakeable polyester film in a form-fill-seal process manufacture.

Additional dual bakeable packaging may include a thermoformable flexible container (eg, a pouch) having an opening made by thermoforming from dual bakeable polyester film that encloses the food product and is identical by self-sealing at the opening or closed by sealing a flexible double bakeable lid around the opening.

Thermoforming is a manufacturing method in which a plastic film is heated to forming temperatures, formed into a specific shape in a mold, cooled and trimmed to produce containers, lids, trays, blisters and others for food, medical and general packaging applications product.

Thermoforming is widely used in food packaging due to process flexibility, packaging speed and ease of automation.

Thermoformed containers, such as pouches or trays, can be pre-manufactured prior to the packaging process, or alternatively, manufactured in-line in a continuous fashion in a thermoformed packaging process.

Typically, in a continuous thermoforming packaging process for high volume, thin gauge products, a plastic film (bottom web) is fed from a roll into an oven for heating to forming temperature. The heated film is then fed to a forming station, where the mold and pressure chambers are closed on the film.

A vacuum is then applied to remove the trapped air and the material is drawn into or onto the mold along with the pressurized air to cause the plastic to form the fine shape of the mold, thereby forming a plurality of concave containers. Once the containers are formed from the bottom web, the product to be packaged is loaded into the container, the air is expelled from the inside, and the package can then be closed by heat sealing the upper portion of each container with a lid (top web), the lid It can be, for example, a non-thermoformed film, another thermoformed flexible container or a stretched film to manufacture a plurality of vacuum-packed products in a continuous manner.

The continuous web comprising the closed package is then transferred to a cutting station where a die cuts the package from the remaining web.

The remaining web is usually wound onto a take-up reel or fed into an in-line pelletizer for recycling.

"Deep drawing" is a particularly desirable thermoforming application, named for the relatively high final depth of formed containers used to form trays, pouches, and similar products.

Films for deep drawing must have several properties suitable for use.

First, since the material is subjected to much higher stretches than conventional thermoforming, it must be endowed with exceptionally high formability.

In fact, when thermoforming deep cavities, the flat sheet that defines the surface must be able to provide a much higher surface of the cavity. When the sheet is heated and pressed into a deep die, it undergoes significant stretching to conform to the cavity shape. As the sheet stretches, it thins and can break.

In addition, the film must conform closely to all details of the mold, maintaining high definition. At the same time, the thermoformed film should not have a so-called "retraction" effect, ie, when removed from the mold, the formed container should retain as much as possible the shape and dimensions given by the mold.

The film must also have good mechanical properties so that the final package, in which the thickness of the packaging material is reduced by the forming step, still has the necessary resistance to mechanical damage.

Known films for deep drawing are generally characterized by the presence of a reinforcing layer, preferably a polyamide layer, such as the laminate shown in WO 2005/063483 in the name of Du Pont. These laminates are not suitable for dual bakeable applications.

WO2012027043A1 in the name of Cryovac also discloses a thermoforming process wherein the thermoformed film is a polyamide based film.

The resulting package according to the definitions given therein (page 1, lines 17-23) will be subjected to exposure to microwaves and conventional heating to a temperature of 375°F or 400°F (ie, 190°C or 204°C) in an oven. However, they will not be suitable for cooking in ovens at temperatures above 205°C and up to 220°C due to the presence of lower melting point resins especially in the outer mechanically damaged layer of the film.

A variant of the thermoforming packaging method commonly used for food packaging is the so-called thermoform-shrink or roll-shrink packaging method. In this application, a thermoplastic heat shrinkable film unwound from a roll is thermoformed in-line, loaded with product, closed, and then heat shrunk around the product.

Thermoforming-shrink wrapping methods typically include:

- heating the bottom web and forcing it into the shape of the mould by means of positive or negative air pressure;

- placing the food product to be packaged within the formed web;

- applying a vacuum and heat sealing the top web on the bottom web so that the package is completely sealed, and finally

- Heat shrink the packaging for a better more attractive appearance.

The top web may or may not be heat shrinkable.

The shrinkage of the packaging material of the bottom web, the top web, or both the bottom web and the top web caused by the heat treatment provides the desired tight appearance for the final vacuum packaging. Examples of such packages are eg those described in EP2030784 in the name of Cryovac, US8424273 in the name of CSF, US2008/0152772 and in US20050173289 in the name of Multivac. The multilayer heat shrinkable films used therein are not polyester based and are not suitable for dual bakeable applications.

In thermoforming-shrinking applications, not only before thermoforming, but especially after thermoforming, the film is required to have optimum shrinkage properties in order to obtain a tight package.

Therefore, once thermoformed, the film must maintain some free heat shrinkage and some shrinkage tension in the LD and TD directions to ensure that after the shrinking step, the package appearance is as tight as desired.

In addition, the film should have good optical properties after stretching and shrinking, not only for purely aesthetic reasons, but also to allow visual inspection of the packaged product.

There are packaging methods known in the literature and recently applied to the food industry that combine deep drawing and then shrinking, ie, which involve deep drawing oriented heat shrinkable films to form flexible shrinkable containers with deep cavities.

These deep draw thermoforming-shrink wrap methods differ from conventional deep draw methods in that a heat shrinkable flexible film is used in place of standard non-heat shrinkable typically thicker laminates. The main advantages provided by deep draw thermoformed shrink wrap with heat shrinkable films are the reduction in the amount of wrapping material used and the improved package appearance making the product more attractive.

Standard dual bakeable oriented PET materials commonly used as lids for tray lids or as non-thermoformable pouches are not suitable as forming webs for thermoforming, especially in deep drawing, because they are imparted with insufficient flexibility. Formability. Also, they are not suitable for shrink applications because they have very poor shrink properties.

To the applicant's knowledge, there are few examples of the use of dual bakeable polyester films in standard (ie, shallow) thermoformed packaging for dual bakeable applications.

For example, document WO 2015/189351 in the name of Cryovac discloses the use of polyester film in the packaging of perishable food products (eg fish) under modified atmosphere to increase the shelf life of the product and allow packaged cooking in the same package. Possible packaging includes a top polyester film and a bottom polyester film that are sealed together and encapsulate the food product. The bottom polyester film may be thermoformed. In the examples, the base film 1 (which was heat set and no longer shrinkable) was formed at a maximum depth of 1 cm (see examples 5 and 6, draw ratios of 1.24 and 1.26, respectively). The packaging of these examples does not contain any product and does not shrink.

Document WO 2006/002263 in the name of DuPont describes thermoformed pouches for packaged cooking applications made under standard thermoforming conditions from polyester-polyamide films comprising specific sulphur-containing polyesters.

To the applicant's knowledge, there are even fewer instances of polyester films being used in deep-drawn food packaging for dual bakeable applications.

Document WO2007/054698 in the name of Du Pont describes a method of packaging fish or meat comprising thermoforming a dual bakeable thermoformable polyester receiver film to provide a cavity into which the product is placed. cavity, and with a double bakeable cover film to seal the package by heat sealing the two films around the product.

The intrinsic viscosity of the copolyesters used in thermoformable films is below 0.75 dl/g (see pages 20-21 of the specification).

In Examples 1-4, double-bakeable polyester films of unknown composition (named Mylar® P25, HFF-FT, HFF-FT3 and HFF-FT7, respectively) were drawn at a depth of 50 mm. These examples do not provide information about the shape, dimensions of the mold and about the draw ratio. The final package is not subject to heat shrinkage.

Compared to the films of the present invention, the formability of these films is not as good as the film obtained in Comparative Example 1 of this specification.

Furthermore, according to the technical data sheet for Mylar® P25, the film shows a percent free shrinkage (ASTM E794) of 2.5% along LD and 1.5% along TD at 150°C, which would not be ideal for thermoforming-shrink wrap applications of. Therefore, as shown in this Example 4, the commercial film designated Mylar® OL25 did not perform well in thermoform-shrink applications, resulting in a wrinkled shrink wrap (Figure 5B).

US20050074598 describes coextruded biaxially oriented polyester films for tray lidding comprising a base layer (B) and a heat-sealable top layer (A), these films are characterized by a particular composition of layer (A) which is Provides heat sealability and peelability when sealed to APET/CPET trays. The document does not disclose the use of these films in any thermoforming application. To the applicant's knowledge, there are no examples of polyester films used in thermoforming-shrink wrapping processes for dual bakeable applications.

In conclusion, there remains a need for dual bakeable highly formable polyester films that are suitable for deep drawing and/or thermoforming-shrink packaging, ie dual bake films that form well in thermoforming and are Resists high draw ratios, does not retract upon release from the mold, and when heat shrinkable, is highly shrinkable after thermoforming, thus providing a very tight, attractive shrink wrap.

SUMMARY OF THE INVENTION

The applicant has surprisingly found that known double bakeable polyester films disclosed in document WO2012/160142 for use as lids in tray lids and in WO2015/189351 as non-thermoformable or Known dual bakeable polyester films for shallow thermoformed non-shrinkable containers perform very well in thermoform packaging applications such as deep draw and thermoform-shrink packaging.

Applicants have found that these films are characterized by unexpectedly high formability, allowing deep drawing even at lower thicknesses than conventional films. Advantageously, the use of thinner membranes results in cost savings and improved carbon footprint.

In addition, these films in their heat-shrinkable form (ie, when not heat-set) exhibit surprisingly high shrinkage after thermoforming, thus providing a very tight package after shrinkage. This is surprising because in general formability and shrinkage are inversely related.

Finally, due to their remarkable heat resistance, these films can provide deep draw and/or shrink wrapping, which is double bakeable even at temperatures above 205°C and up to 220°C, which is important for some tape wraps Cooking applications are particularly popular.

Therefore, the first object of the present invention is a thermoformed food packaging method for the manufacture of a dual bakeable thermoformed packaging, comprising:

- to provide a thermoformable bibakeable biaxially oriented polyester film as the bottom web,

- forming the bottom web so as to provide at least a cavity with openings;

- placing food product in said cavity through said opening;

- at the opening, by air-tight sealing the bottom web itself or by providing a dual-bakeable top web and hermetically sealing the dual-bakeable top web around the opening sealing to the bottom web to close the cavity; and

- cut out said sealed package,

characterized in that the bottom web comprises:

outer heat-sealable polyester layer a),

An inner polyester base layer b) comprising a polyester having an intrinsic viscosity (IV), measured according to ASTM D4603-03, of higher than 0.75 dl/g,

outer polyester layer c), and

i) the bottom web is formed with a draw ratio higher than 1.26, or

ii) The bottom web is heat shrinkable and the sealed package is eventually heat shrunk.

A second object according to the present invention is a dual bakeable thermoformable flexible container comprising a thermoformed cavity and an opening, made by thermoforming a film of the bottom web as described above, wherein the thermoformed cavity is The depth is greater than 1 cm and/or the thermoformed container is heat shrinkable.

A third object according to the present invention is a dual bakeable airtight thermoformed package comprising

A dual bakeable thermoformable flexible container according to a second object, comprising a thermoformed cavity and an opening,

food placed in said cavity,

The opening is hermetically closed by a flexible container that is self-sealing at the opening or by a dual bakeable top web sealed around the opening to the container.

A fourth object of the present invention is a method for cooking food comprising

- according to the third embodiment above, there is provided a dual bakeable thermoformable package enclosing said product, and

- Cooking the packaged food in the package in a microwave or conventional oven.

Description of drawings

Figure 1 shows a cross section of a deep drawn container (201) according to the invention;

Figure 2 shows pictures of thermoformed containers 2A, 2B made of commercial films (Mylar OL25 and Mylar OL40) and thermoformed container 2C made of film 7 suitable for use in the present invention;

Figure 3 is a scheme of the "thermoforming-shrinking" process;

Fig. 4 is a picture of a sausage thermoformed package according to the present invention (Fig. 4A, left) and a comparative package (Fig. 4B, right) before shrinking;

Figure 5 is a picture of the same sausage thermoformed package of Figure 4 but after shrinking (package according to the invention, Figure 5A, left; and comparative package, Figure 5B, right).

definition

As used herein, the term "film" refers to a plastic web, whether it is a film or sheet or a tube.

As used herein, the terms "inner layer" and "inner layer" refer to any film layer whose two major surfaces are directly adhered to another layer of the film.

As used herein, the phrase "outer layer" or "outer layer" refers to any film layer whose only one major surface is directly adhered to another layer of the film. As used herein, the phrases "seal layer," "sealing layer," and "sealant layer" refer to sealing of a film with itself, with another layer of the same or another film the outer layer.

As used herein, the term "base layer" refers to the layer representing the largest portion of the film in terms of thickness, in particular a film layer having a thickness of at least 40%, preferably at least 50%, more preferably at least 60% of the total film thickness.

As used herein, the term "adhered" refers to a film layer having a major surface, either directly or indirectly (through one or more additional layers therebetween) by coextrusion, extrusion coating, or by adhesive lamination touch each other.

As used herein, "directly adhered" film layers have major surfaces in direct contact with each other, with no adhesive or other layers in between.

As used herein, the term "polymer" refers to the product of a polymerization reaction, and includes both homopolymers and copolymers.

As used herein, the term "homopolymer" refers to a polymer obtained by polymerizing a single monomer, ie, a polymer consisting essentially of a single type of polymer (ie, repeating units).

As used herein, the term "copolymer" refers to a polymer formed by the polymerization of at least two different monomers. For example, the term "copolymer" includes the copolymerization reaction product of ethylene and an alpha-olefin such as 1-hexene. When used in generic terms, the term "copolymer" also includes, for example, terpolymers. The term "copolymer" also includes random copolymers, block copolymers and graft copolymers.

As used herein, the term "polyolefin" refers to any polymeric olefin, which may be linear, branched, cyclic, aliphatic, aromatic, substituted or unsubstituted. Polyolefins include olefin homopolymers, olefin copolymers, copolymers of olefins and non-olefinic comonomers copolymerizable with the olefins, such as vinyl monomers, modified polymers thereof, and the like. Specific examples include ethylene homopolymers, propylene homopolymers, butene homopolymers, ethylene alpha-olefin copolymers, etc., propylene/alpha-olefin copolymers, butene/alpha-olefin copolymers, ethylene/unsaturated esters Copolymers (eg, ethylene/ethyl acrylate, ethylene/butyl acrylate, ethylene/methyl acrylate), ethylene/unsaturated acid copolymers (eg, ethylene/acrylic acid, ethylene/methyl acrylate) acrylic copolymer), ethylene/vinyl acetate copolymer, ionomer resin, polymethylpentene, etc.

As used herein, the term "ethylene/alpha-olefin copolymer" refers to both heterophasic and homogeneous polymers, such as linear low density polymers having densities generally in the range of about 0.900 g/ ^cm3 to about 0.930 g/ ^cm3 Ethylene (LLDPE), linear medium density polyethylene (LMDPE) with densities typically in the range of about 0.930 g/cm ³ to about 0.945 g/cm ³ and densities below about 0.915 g/cm ³ , typically 0.868 g/cm ³ Very low and ultra-low density polyethylenes (VLDPE and ULDPE) in the range to 0.915 g/ ^cm3 , and metallocene catalyzed Exact® and Exceed® homogeneous resins such as available from Exxon, single-site available from Dow Affinity® resins and Tafmer® homogeneous ethylene/alpha-olefin copolymer resins available from Mitsui. All of these materials typically include copolymers of ethylene with one or more comonomers selected from C4-10 alpha-olefins such as butene-1, hexene-1, octene-1, etc., wherein the copolymers have Molecules include long chains or cross-linked structures with relatively few side chain branches.

As used herein, the phrase "heterophasic polymer" or "polymer obtained by heterogeneous catalysis" refers to a polymerization reaction product that varies relatively widely in molecular weight and in composition distribution, ie, using, for example, conventional Ziegler-Nano Typical polymers prepared with column catalysts, for example, metal halides activated by organometallic catalysts, i.e., titanium chloride optionally containing magnesium chloride complexed with trialkylaluminum, and can be described in patents such as Goeke et al. No. 4,302,565 and US Patent No. 4,302,566 to Karol et al. Heterophasically catalyzed copolymers of ethylene and alpha-olefins may include linear low density polyethylene (LLDPE), very low density polyethylene (VLDPE) and ultra low density polyethylene (ULDPE). Some copolymers of the type described are available, for example, from the Dow Chemical Company of Midland, Michigan, USA and are sold under the trademark Dowlex® resins.

As used herein, the phrase "homogeneous polymer" or "polymer obtained by homogeneous catalysis" or "single site catalyzed (ssc) polymer" refers to a polymerization reaction product of relatively narrow molecular weight distribution and relatively narrow composition distribution. Homogeneous polymers differ structurally from heterophasic polymers in that homogeneous polymers exhibit relatively uniform comonomer sequences within the chains, mirror image distribution of sequences throughout the chains, and similar lengths across the chains, That is, a narrow molecular weight distribution. The term includes those homogeneous polymers prepared using metallocene or other single site type catalysts (ssc), as well as those obtained under homogeneous catalytic conditions using Ziegler-Natta type catalysts. US Patent No. 5,026,798 to Canich describes the copolymerization of ethylene and alpha-olefins under homogeneous catalysis including, for example, copolymerization with a metallocene catalyzed system including a constrained geometry catalyst, ie, a monocyclopentadienyl transition metal complex.

Homogeneous ethylene/alpha-olefin copolymers (homogeneous EAOs) include modified or unmodified linear homogeneous ethylene/alpha-olefin copolymers sold as Tafmer® resins by Mitsui Petrochemical Corporation of Tokyo, Japan, manufactured by Texas Instruments, USA Modified or unmodified linear homogeneous ethylene/alpha-olefin copolymers sold as Exact® resins by Exxon Mobil Chemical Company of Houston, SL and modified with long chain branching sold by Dow Chemical Company as Affinity® brand resins. A homogeneous or unmodified ethylene/α-olefin copolymer. As used herein, "long-chain branched" ethylene/alpha-olefin copolymers refer to copolymers having branches of length commensurate with the length of the polymer backbone. The long chain branched ethylene/alpha-olefin copolymer has an I10/I2 ratio of at least 6, or at least 7, or 8 to 16 (ie, the ratio of melt index at 10 kg to melt index at 2.16 kg) .

As used herein, the term "modified" refers to chemical derivatives, such as derivatives having any form of anhydride functionality, such as maleic anhydride, crotonic anhydride, citraconic anhydride, itaconic anhydride, fumaric anhydride, and the like, whether Grafted onto a polymer, either copolymerized with a polymer, or blended with one or more polymers, and also includes derivatives of such functional groups, such as acids, esters and metal salts derived therefrom.

As used herein, the phrase "modified polymer" and more specific phrases such as "modified ethylene/vinyl acetate copolymer" and "modified polyolefin" refer to those having grafted thereon and/or therewith Such polymers of anhydride functional groups as just defined above are copolymerized and/or blended therewith. Preferably, such modified polymers have anhydride functional groups grafted onto or polymerized therewith rather than merely blended therewith.

As used herein, the phrases "anhydride-containing polymer" and "anhydride-modified polymer" refer to one or more of the following polymers: (1) obtained by copolymerizing an anhydride-containing monomer with a second, different monomer and (2) anhydride-grafted copolymers, and (3) mixtures of polymers and anhydride-containing compounds.

As used herein, the term "modified polyolefin" includes copolymerization of olefin homopolymers or copolymers thereof with unsaturated carboxylic acids such as maleic acid, fumaric acid, etc. or derivatives thereof such as anhydrides, esters or metal salts, etc. The prepared modified polymer. It also includes the incorporation of unsaturated carboxylic acids such as maleic acid, fumaric acid, etc., or derivatives thereof such as anhydrides, esters or metal salts, etc., into olefin homopolymers or copolymers, by blending or bonding with polymer chains. A modified polymer obtained by branching onto the polymer chain.

Ethylene-unsaturated acid polymers include homopolymers and copolymers having acrylic and/or methacrylic linkages between monomer units. Acrylic-based resins can be formed by any method known to those skilled in the art and can include the polymerization of acrylic or methacrylic acid in the presence of light, heat or catalysts such as benzoyl peroxide, or by esters of these acids followed by saponification form. Examples of acrylic-based resins include, but are not limited to, ethylene/acrylic acid copolymers (EAA), ethylene/methacrylic acid copolymers (E/AA), and blends thereof.

Ethylene-unsaturated ester polymers include homopolymers and copolymers of esters having acrylic linkages between monomer units. Acrylate-based resins may be formed by any method known to those skilled in the art, such as by polymerizing acrylate monomers in the same manner as described for acrylic-based resins. Examples of acrylate-based resins include, but are not limited to, methyl/methacrylate copolymer (MMA), ethylene/vinyl acrylate copolymer (EVA), ethylene/methacrylate copolymer (EMA), ethylene/acrylic acid n-Butyl ester copolymer (EnBA) and blends thereof.

As used herein, the phrase "ethylene/vinyl acetate" (EVA) refers to a copolymer formed from ethylene and vinyl acetate monomers in which ethylene units are present in large amounts and vinyl acetate units are present in small amounts. Typical amounts of vinyl acetate may range from about 5% to about 20% by weight.

As used herein, the term "ionomer resin" refers to a copolymer based on a metal salt of ethylene and a copolymer of vinyl monomers having acid groups, such as methacrylic acid, and is one in which the bonds are ionic (ie, chain ionic bonds) and covalent bonds. Ionomer resins have positively and negatively charged groups that are not associated with each other, thereby imparting polar character to the resin. The metals may be in the form of monovalent or divalent ions such as lithium, sodium, potassium, calcium, magnesium and zinc. Unsaturated organic acids include acrylic acid and methacrylic acid. Unsaturated organic esters include methacrylate and isobutyl acrylate. The ionomer resin may comprise a mixture of two or more ethylene/unsaturated organic acid or ester copolymers.

As used herein, the term "polyester" generally refers to a homopolymer or copolymer having ester linkages between monomer units, which may be formed, for example, by a polycondensation reaction between a dicarboxylic acid and a diol. The term "polyester" refers to both homopolyesters and copolyesters, wherein a homopolyester is defined as a polymer obtained by the condensation of a dicarboxylic acid with a diol, and a copolyester is defined as a A polymer obtained by the condensation of various dicarboxylic acids with one or more diols.

Ester monomer units can be represented by the general formula: R-C(O)O-R', where R and R' = alkyl, and can typically be composed of dicarboxylic acid and diol monomers or contain both carboxylic acid and hydroxyl moieties polymerization of the monomers. The dicarboxylic acids may be straight chain or aliphatic, i.e. oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, etc.; or may be Aromatic or alkyl-substituted aromatic acids, i.e., various isomers of phthalic acid, such as paraphthalic acid (or terephthalic acid), isophthalic acid, and naphthalene Diformic acid. Specific examples of alkyl-substituted aromatic acids include various isomers of dimethylphthalic acid, such as dimethylisophthalic acid, dimethylphthalic acid, dimethylterephthalic acid, dimethy Various isomers of ethylphthalic acid, such as diethylisophthalic acid, diethylphthalic acid, various isomers of dimethylnaphthalene dicarboxylic acid, such as 2,6-dimethyl Naphthalenedicarboxylic acid and 2,5-dimethylnaphthalene dicarboxylic acid, and various isomers of diethylnaphthalene dicarboxylic acid. Diols can be straight chain or branched. Specific examples include ethylene glycol, propylene glycol, propylene glycol, 1,4-butanediol, neopentyl glycol, and the like. Polyalkyl terephthalate is an aromatic ester having a benzene ring, wherein compared to polyalkyl isophthalate in which two ester bonds are present on the 1,3-carbon of the benzene ring, the The 1,4-carbon has an ester bond. In contrast, polyalkyl naphthalates are aromatic esters with two fused benzene rings, where the two ester linkages can be present at the 2,3-carbon or the 1,6-carbon.

As used herein, unless otherwise stated, the term "polyester layer, film or container" means comprising a substantial proportion of polyester, ie comprising greater than 50% by weight, preferably greater than 60% by weight, 70% by weight relative to the layer or film, respectively %, 80% by weight, 90% by weight of polyester layer, film or container.

As used herein, intrinsic viscosity (IV) is defined as the limit of reduced viscosity at infinite dilution of a polymer, and is determined using a capillary viscometer. A suitable method for determining intrinsic viscosity is ASTM method D4603-03.

As used herein, the term "major proportion" of resin in a layer, film or container means that greater than 50% by weight of said resin is present in said layer, film or container.

As used herein, the term "small proportion" of resin in a layer, film or container means that less than 50% by weight of said resin is present in said layer, film or container.

As used herein, the term "thermoformed flexible container" refers to a thermoformed flexible pouch having an opening for holding the product to be packaged.

As used herein, the phrases "machine direction", abbreviated herein as "MD", and "machine direction", abbreviated herein as "LD", refer to the direction "along the length of the film", ie, in the extrusion direction of the film superior.

As used herein, the phrase "transverse direction", abbreviated herein as "TD", refers to the direction across the film, perpendicular to the machine direction or machine direction.

As used herein, the term "extrusion" refers to the process of forming a continuous shape by forcing molten plastic material through a die, followed by cooling or chemical hardening. Immediately prior to extrusion through the die, the relatively high viscosity polymeric material is fed to a variable pitch rotating screw, ie, an extruder, which forces the polymeric material through the die.

As used herein, the term "co-extrusion" refers to the process of extruding two or more materials through a single die having two or more orifices arranged such that the extrudates meet and are They are fused together to form a sheet-like structure and then frozen, ie, quenched.

As used herein, the term "oriented" means that the thermoplastic web is drawn in one direction ("uniaxial") or in both directions ("biaxial") at a temperature above the softening temperature, and then the film is cooled so that it "Shape" while substantially maintaining the drawn dimensions. Solid-state orientation at temperatures above the softening point produces films that exhibit thermal shrinkage characteristics upon subsequent heating. Orientation in the molten state, as in the manufacture of blown films, does not result in heat shrinkable films. Orientation in both the molten state and the solid state increases the degree of polymer chain alignment, thereby enhancing the mechanical properties of the resulting oriented films.

As used herein, the term "vacuum forming" is a thermoforming process in which air is evacuated from the sealed space between the hot sheet and the mold, allowing atmospheric pressure to force the sheet to conform to the contours of the mold.

As used herein, the term "standard thermoforming or shallow thermoforming" refers to thermoforming characterized by a low draw ratio, ie, below 1.26, which provides a shallow cavity.

As used herein, "deep drawing or deep drawing thermoforming" generally refers to the thermoforming of thermoplastic materials characterized by a draw ratio higher than 1.26, preferably higher than 2.0, 2.5, 3.0, 3.5, 4.0 or 4.5, which provides deep cavity.

As used herein, the term "thermoformable" is defined as a material that can be "thermoformable" after being heated on suitable equipment, ie, a material that can be formed after exposure to pressure and/or vacuum. The material is thermoplastic such that it deforms when heated, but exhibits sufficient dimensional stability at room temperature to maintain the shape predetermined by thermoforming.

As used herein, the term "deep drawable" is defined as a material that can be drawn at a draw ratio above 1.26, preferably above 2.0, more preferably above 2.5, 3.0, 3.5, 4.0 or 4.5.

As used herein, the term "thermoforming draw ratio" (DR) refers to the draw ratio calculated on the mold, in particular the ratio between the total surface area of the mold and the footprint of the mold.

As used herein, the term "actual thermoforming draw ratio" (a-DR) refers to the actual ratio by which a film is stretched under thermoforming. The actual stretch ratio can be calculated based on the actual size of the thermoformed container.

As used herein, the term "cavity" refers to a recessed portion obtainable by thermoforming a thermoplastic material surrounded by a raised outer or peripheral portion.

As used herein, the terms "heat-shrinkable", "heat-shrinkable" and the like refer to the tendency of a film to shrink when heated, ie, shrink when heated, such that when the film is in an unconstrained state, the size of the film decreases. Free shrinkage is the percent change in dimension of a 12 cm x 12 cm film sample when heated in an oven at 180°C for 5 minutes, as explained in this Test Methods section.

As used herein, unless otherwise stated, the terms "heat shrinkage" or "% free shrinkage" refer to the shrinkage properties of a film prior to thermoforming.

As used herein, the term "non-heat shrinkable" refers to a film characterized by a total free shrinkage percentage (ie, the sum of the free shrinkage percentages in the LD and TD directions) of less than 5%, as reported in the experimental section Test methods are measured in an oven at 180°C.

As used herein, the term "microwaveable" refers to "substantially microwave-transparent" structures as well as "microwave-active" structures. While substantially microwave transparent are those structures capable of being passed through at least 80%, preferably at least 90%, of microwaves generated by microwave ovens without any interference therewith, microwave activity is the combination of energy designed to alter adjacent food products those structures of the deposited microwave reflective components. For "microwaveable" in both cases, the packaging material should not degrade or deform under the conditions of use, and it should not release more than 60 ppm of bulk contaminants to the packaged food it comes in contact with. In fact, according to most food laws, packaging materials that are subjected to 30 minutes of heat treatment at 121°C (a sufficiently vigorous condition not normally achieved in microwave cooking) without deforming and releasing less than 60 ppm of contamination are considered "microwaveable" processed".

As used herein, the term "dual bakeable" refers to a film or packaging suitable for both microwave cooking and conventional oven cooking, which is capable of withstanding cooking temperatures above 205°C and up to 220°C.

All percentages in this specification are weight percentages unless otherwise stated.

Detailed ways

The first object of the present invention is a thermoformed food packaging method for the manufacture of a dual bakeable thermoformed packaging, comprising:

- to provide a thermoformable bibakeable biaxially oriented polyester film as the bottom web,

- forming the bottom web so as to provide at least a cavity with openings;

- placing food product in said cavity through said opening;

- at the opening, by air-tight sealing the bottom web itself or by providing a dual-bakeable top web and hermetically sealing the dual-bakeable top web around the opening sealing to the bottom web to close the cavity; and

- cut out said sealed package,

characterized in that the bottom web comprises:

outer heat-sealable polyester layer a),

An inner polyester base layer b) comprising a polyester having an intrinsic viscosity (IV), measured according to ASTM D4603-03, of higher than 0.75 dl/g,

outer polyester layer c), and

i) the bottom web is formed with a draw ratio higher than 1.26, or

ii) The bottom web is heat shrinkable and the sealed package is eventually heat shrunk.

The outer heat-sealable polyester layer a) of the film comprises at least 80% by weight, preferably at least 85% by weight of one or more polyesters, relative to the weight of the layer.

The composition of the heat-sealable polyester layer a) may vary to some extent, provided that it is sealed to the polyester material at a temperature below the melting temperature of the resins of the base layer b) and the outer layer c).

The seal must be strong enough to prevent the package from leaking during storage and transport, but at the same time it must allow for self-venting during cooking and easy opening of the package by the end consumer after cooking.

Suitable heat-sealable polyester compositions for layer a) are known and described, for example, in WO2007093495 or WO2012160142.

In one embodiment, according to WO2007093495, the polyester of the heat sealable layer a) may be an amorphous polyester or a crystalline polyester, the melting temperature of which is not higher than that of the polyester of the base layer b), or a mixture thereof.

The term "crystalline" is used herein to indicate that a resin has a defined melting temperature.

The heat sealable layer a) may comprise an amorphous copolyester resin or a crystalline copolyester resin having a melting temperature lower than that of the polyester of the base layer b).

As polyester resin for the heat-sealable layer a), it is possible to use one or more dicarboxylic acids or their lower alkyl (up to 14 carbon atoms) diesters with one or more diols, especially aliphatic or cycloaliphatic diol derived copolyester resins.

Suitable dicarboxylic acids include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid or 2,5-, 2,6- or 2,7-naphthalene dicarboxylic acids, and aliphatic dicarboxylic acids Carboxylic acids, such as succinic acid, sebacic acid, adipic acid, azelaic acid, suberic acid or pimelic acid. Suitable diols include aliphatic diols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 2 , 2-dimethyl-1,3-propanediol, neopentyl glycol and 1,6-hexanediol, and cycloaliphatic diols such as 1,4-cyclohexanedimethanol and 1,4-cyclohexanediol alcohol.

In one embodiment, according to WO2007093495, the heat sealable layer a) comprises a crystalline copolyester.

Crystalline copolyesters refer to copolyesters having at least one distinct melting peak in a differential scanning calorimetry (DSC) thermogram. The melting point of the resin can be measured by using the DSC technique according to ASTM D3418.

Preferably, the crystalline copolyester of the heat sealable layer comprises aromatic dicarboxylic acids and aliphatic dicarboxylic acids. The preferred aromatic dicarboxylic acid is terephthalic acid. Preferred aliphatic dicarboxylic acids are selected from sebacic acid, adipic acid and azelaic acid. The concentration of aromatic dicarboxylic acid present in the copolyester is preferably in the range of 45 to 80 mol %, more preferably in the range of 50 to 70 mol %, based on the dicarboxylic acid component of the copolyester , and especially in the range of 55 mol % to 65 mol %. The concentration of the aliphatic dicarboxylic acid present in the copolyester is preferably in the range of 20 mol % to 55 mol %, more preferably in the range of 30 mol % to 50 mol %, based on the dicarboxylic acid component of the copolyester , and especially in the range of 35 mol % to 45 mol %. Particularly preferred examples of suitable copolyesters are (i) copolyesters of azelaic and terephthalic acids with aliphatic diols, preferably ethylene glycol; (ii) adipic and terephthalic acids with aliphatic diols; A diol, preferably a copolyester of ethylene glycol; and (iii) a copolyester of sebacic acid and terephthalic acid with an aliphatic diol, preferably butanediol. Preferred copolyesters include copolyesters of sebacic acid/terephthalic acid/butanediol with a melting point Tm of 117°C, and azelaic acid/terephthalic acid/ethylene glycol with a Tm of 150°C ester.

In one embodiment, according to WO2007093495, the copolyester of the heat-sealable layer a) is derived from aliphatic diols and various aromatic dicarboxylic acids, in particular terephthalic acid and isophthalic acid. Preferred copolyesters are derived from ethylene glycol, terephthalic acid and isophthalic acid. The preferred molar ratio of the terephthalic acid component to the isophthalic acid component is in the range of 50:50 to 90:10, preferably in the range of 65:35 to 85:15.

In one embodiment, according to WO2007093495, the heat sealable layer a) comprises an amorphous copolyester.

Suitable amorphous copolyesters are those derived from aliphatic and cycloaliphatic diols with one or more dicarboxylic acids, preferably aromatic dicarboxylic acids. Typical polyesters that provide satisfactory heat sealability include copolyesters of terephthalic acid with aliphatic and cycloaliphatic diols, especially ethylene glycol and 1,4-cyclohexanedimethanol. The preferred molar ratio of cycloaliphatic diol to aliphatic diol is in the range from 10:90 to 60:40, preferably in the range from 20:80 to 40:60, and more preferably in the range from 30:70 to 35:65 In the range. An example of such a copolyester is PETG Eastar 96763 sold by Eastman, which comprises a copolyester of terephthalic acid, about 33 mole % 1,4-cyclohexanedimethanol, and about 67 mole % ethylene glycol, and Its glass transition temperature Tg was 81°C.

In order to reduce the sealing strength and thus facilitate the opening of the package, it is convenient to combine the one or more polyester resins of the heat-sealable outer layer a) with 3 to 40% by weight, 5 to 30% by weight, preferably 15 to 25% by weight of Suitable thermoplastic resins are blended. Suitable thermoplastic resins to help reduce seal strength without compromising the optical properties of the film are polyamides, polystyrenes, especially styrene-butadiene block copolymers, ionomers, ethylene/unsaturated carboxylic acid copolymers , such as ethylene/(meth)acrylic acid copolymers, ethylene/unsaturated ester copolymers such as ethylene/vinyl acetate copolymers, maleic anhydride modified polyethylene, ethylene/propylene copolymers and ethylene/cyclic olefin copolymers , such as ethylene/norbornene copolymers.

By blending the amorphous copolyester with 3 to 40% by weight of ethylene/acrylic acid copolymer or ethylene/propylene copolymer or maleic anhydride-modified polyethylene, it is possible to obtain airtightness of the seal and the stability of the package upon opening. A good balance between easy membrane removal. Good results can be obtained by blending PET with 3 to 40% by weight of polyamide. Suitable polyamides are, for example, polyamide 6, polyamide 66 and copolyamides, including copolyamide 6/9, copolyamide 6/10, copolyamide 6/12, copolyamide 6/66, copolyamide 6/69, and aramid family of polyamides and copolyamides such as 61, 6I/6T, MXD6, MXD6/MXDI.

Blends of amorphous copolyesters with 3 to 40% by weight of ethylene/acrylic acid copolymers are particularly suitable for packaging applications that require heat treatment such as pasteurization, as they provide a balance between ease of opening and air tightness of the package. best balance. An example of a suitable amorphous polyester is PETG Eastar® 6763 sold by Eastman.

According to WO2012160142, when heating or cooking at higher temperatures in a conventional oven is required, the heat sealable layer a) in addition to comprising about 25% to 70% by weight of at least a first amorphous polyester having a melting temperature not higher than Melting temperature of the polyester of the base layer b)) and 10 to 20% by weight of at least one thermoplastic resin, 20 to 60% by weight of at least one further polyester resin (ternary blend) .

Suitable amorphous polyester resins are those derived from aliphatic and cycloaliphatic diols with one or more dicarboxylic acids, preferably aromatic dicarboxylic acids. Preferably, the amorphous polyester is selected from those polyesters derived from aliphatic and cycloaliphatic diols and a dicarboxylic aromatic acid, more preferably terephthalic acid. Preferred amorphous polyesters are copolyesters of terephthalic acid with aliphatic and cycloaliphatic diols, especially ethylene glycol and 1,4-dicyclohexanedimethanol.

The preferred molar ratio of cycloaliphatic diol to aliphatic diol is in the range of 10:90 to 60:40, preferably in the range of 20:80 to 40:60, more preferably in the range of 30:70 to 35:65 within the range. A specific example of a particularly preferred amorphous polyester is PETG Eastar® 6763 sold by Eastman, which comprises a copolymer of terephthalic acid, about 33 mole % 1,4-cyclohexanedimethanol and about 67 mole % ethylene glycol ester.

In a particularly preferred embodiment, the amorphous polyester resin in the heat-sealable layer is the same polyester resin used in the base layer.

Suitable thermoplastic resins are polyamides, polystyrene, especially styrene-butadiene block copolymers, polyethylene, ionomers, ethylene/unsaturated carboxylic acid copolymers, such as ethylene/(meth)acrylic acid copolymers compounds, ethylene/unsaturated ester copolymers such as ethylene/vinyl acetate copolymers, ethylene/propylene copolymers, maleic anhydride modified polyethylenes such as modified LLDPE and ethylene/cyclic olefin copolymers such as ethylene/polyethylene bornene copolymer. Ethylene/(meth)acrylic acid copolymers and modified LLDPE are preferred. Specific examples of particularly preferred thermoplastic resins are Primacor 3440 sold by Dow, which is an ethylene/acrylic acid copolymer with a comonomer acrylic acid content of 9.7%, and BYNEL 4104 (2006) sold by DuPont, which is a maleic anhydride modified ethylene /Butene copolymer and modified LLDPE.

Suitable further polyesters are those derived from one or more aliphatic diols, preferably ethylene glycol and/or cyclohexanedimethanol, and aromatic dicarboxylic acids, preferably terephthalic acid. Suitable further polyesters are preferably characterized by an intrinsic viscosity of at least 0.75 dl/g or higher and/or an intrinsic viscosity with a glass transition temperature Tg of not higher than 80°C and/or a melting point of higher than 240°C. A suitable method for determining intrinsic viscosity is ASTM method D4603-03. A suitable method for determining glass transition temperature is, for example, ASTM method D-3418. A suitable method for determining melting point is, for example, ASTM method D3418.

Polyethylene terephthalate (PET) is preferred. Specific examples of other polyesters are PET sold by Eastman Chemical under the name Eastapak copolyester 9921, or RAMAPET N180 sold by Indorama Polyester.

The amount of the first amorphous polyester in the heat-sealable layer of the multilayer film according to the invention is generally 25 to 70% by weight, preferably 40 to 60% by weight, relative to the total weight of the heat-sealable layer . Particularly preferred amounts are about 40% by weight and about 60% by weight.

The amount of thermoplastic resin in the heat-sealable layer of the multilayer film according to the present invention is generally 10% to 20% by weight, preferably about 15% by weight, relative to the total weight of the heat-sealable layer.

The amount of other polyesters in the heat-sealable layer of the multilayer film according to the invention is generally 20 to 60% by weight, preferably 25 to 50% by weight, relative to the total weight of the heat-sealable layer. Specific preferred amounts are about 25%, about 45%, and about 60% by weight.

In a preferred embodiment, the heat sealable layer a) comprises about 25 to 70% by weight of amorphous polyester, 10 to 20% by weight of thermoplastic resin and 20 to 60% by weight of other polyesters.

In a particularly preferred embodiment, the heat sealable layer a) comprises about 40 to 60% by weight of the first amorphous polyester, 25 to 50% by weight of the other polyester and 10 to 20% by weight of the thermoplastic resin.

Specific examples of blends of at least amorphous polyesters, at least thermoplastic resins and at least other polyesters in heat sealable layer a) are:

i) 60% of the first amorphous polyester; 15% of thermoplastic resin; 25% of other polyesters;

ii) first amorphous polyester 40%; thermoplastic resin 15%; other polyester 45%; and

iii) First amorphous polyester 25%; thermoplastic resin 15%; other polyesters 60%.

A particularly preferred ternary blend of layer a) consists of 60% PETG, 15% modified LLDPE and 25% PET.

Another particularly preferred ternary blend of layer a) consists of 60% by weight of PETG, 15% of ethylene/acrylic acid copolymer and 25% of PET.

Preferably, the thickness of the sealing layer (a) is 0.5 to 25 microns, preferably 1 to 20 microns, more preferably 1 to 15 microns, even more preferably 2 to 10 microns.

The percentage of the thickness of the heat-sealable polyester layer a) to the total thickness of the film is generally 2 to 30%, preferably 3 to 25% or 6 to 20%.

The percentage of heat sealable polyester layer a) thickness to total film thickness is typically below 30%, below 25%, below 20%, below 15% or below 10%.

The inner polyester base layer b) used in the film of the present invention comprises at least a polyester having an intrinsic viscosity higher than 0.75 dl/g as measured according to ASTM D4603-03.

Preferably, the base layer of the film comprises a polyester with an intrinsic viscosity higher than 0.78, more preferably at least 0.80 dl/g.

The polyester resin used as starting material for the base layer b) can also have an intrinsic viscosity below 0.75 dl/g, provided that its intrinsic viscosity after extrusion is higher than said value. For example, the intrinsic viscosity of polyester resins can be increased during the extrusion process by suitable additives such as so-called "chain extenders". Suitable chain extenders are for example those described in EP372846.

A suitable polyester resin is, for example, a polyester of ethylene glycol and terephthalic acid, ie poly(ethylene terephthalate) (PET). Preferred are polyesters comprising ethylene units and comprising at least 90 mole %, more preferably at least 95 mole % terephthalate units, based on dicarboxylate units. The remaining monomer units are selected from other dicarboxylic acids or diols. Suitable further aromatic dicarboxylic acids are preferably isophthalic acid, phthalic acid, 2,5-, 2,6- or 2,7-naphthalenedicarboxylic acid. Among the cycloaliphatic dicarboxylic acids, mention should be made of cyclohexanedicarboxylic acid (especially cyclohexane-1,4-dicarboxylic acid). Among the aliphatic dicarboxylic acids, (C3-C19)alkanedioic acids are particularly suitable, especially succinic acid, sebacic acid, adipic acid, azelaic acid, suberic acid or pimelic acid.

Suitable further aliphatic diols are, for example, aliphatic diols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol Diols, 2,2-dimethyl-1,3-propanediol, neopentyl glycol and 1,6-hexanediol, and cycloaliphatic diols such as 1,4-cyclohexanedimethanol and 1,4 - cyclohexanediol, a heteroatom-containing diol optionally having one or more rings.

Mixtures or blends of homopolyesters and/or copolyesters can be used for the base layer b), provided that polyesters with an IV above 0.75 dl/g constitute a substantial proportion of the base layer. Based on the total weight of the base layer, the base layer b) comprises more than 50% by weight, preferably more than 60% by weight, 70% by weight, 80% by weight, 85% by weight, 90% by weight or 95% by weight of an IV above 0.75 dl/ g of polyester. Any homopolyester and/or copolyester can be blended in the base layer b) with a polyester resin having an IV above 0.75 dl/g.

Preferably, the base layer comprises more than 50%, 60%, 70%, 80%, 85%, 90% or 95% by weight of PET having an IV of at least 0.80 dl/g.

Examples of polyesters suitable for layer b) are PET 9921W® sold by Voridian, RAMAPET N180 from Indorama, which has a melting point Tm of 245°C and an IV of 0.80 dl/g, or EASTAPAK 9921 sold by Eastman Chemical, which has a Tm of 238 °C and IV was 0.8 dl/g.

A suitable mixture for base layer b) may comprise at least 50%, 60%, 70%, 80%, 85%, 90%, 95% of polyester resins with an IV above 0.75 dl/g and not more than 50%, 40% %, 30%, 20%, 15%, 10%, 5% of amorphous polyester resin. The amorphous polyester used in the base layer can be the same or different from the amorphous polyester used in the heat sealable layer.

Amorphous polyester resins suitable for use in the base layer are copolyesters of terephthalic acid with aliphatic and cycloaliphatic diols, especially ethylene glycol and 1,4-cyclohexanedimethanol, such as PETG sold by Eastman Chemical Eastar 6763.

Suitable base layers b) comprise at least 50%, 60%, 70%, 80%, 85%, 90%, 95% of polyester resins with an IV above 0.75 dl/g and not more than 50%, 40%, 30% , 20%, 15%, 10%, 5% of the amorphous polyester of terephthalic acid with ethylene glycol and 1,4-cyclohexanedimethanol.

In one embodiment, layer b) consists of polyester.

The selection of polyesters with intrinsic viscosities higher than 0.75 dl/g for the base layer b) of the films according to the invention provides unexpectedly good formability, high draw ratio, very good compared to commercial films based on conventional polyesters It conforms to the mold well, has minimal shrinkage effects on removal from the mold, and has high shrinkage after thermoforming, as shown in Examples 1, 2, and 4 of the present invention.

The thermoformability of the film can be further improved by preferably incorporating a plasticizer in the base layer. Suitable plasticizers include aromatic dicarboxylates such as dimethyl phthalate, diethyl phthalate, di-n-butyl phthalate, di-n-hexyl phthalate, Di-n-heptyl formate, di-2-ethylhexyl phthalate, di-n-octyl phthalate, di-n-nonyl phthalate, diethyl isophthalate, di-n-octyl phthalate Butyl, di-2-ethylhexyl isophthalate, diethyl terephthalate, di-n-butyl terephthalate, di-2-ethylhexyl terephthalate, etc.; phosphoric acid esters, such as phosphoric acid Triethyl, tri-n-butyl phosphate, trioctyl phosphate, cresyl phosphate, etc.; sebacates, such as dimethyl sebacate, diethyl sebacate, di-n-butyl sebacate, sebacate Dipentyl acid, etc; Acetyl esters, etc.; and polyethylene glycols, etc.

In one embodiment, the plasticizers are selected from aromatic dicarboxylates (especially phthalates) because they have excellent heat resistance, can significantly improve thermoformability, and are There were no problems with sublimation and oozing during the process.

The melting point of the plasticizer is preferably at least 300°C or higher, more preferably at least 350°C. The content of plasticizer in the layer is preferably from 0.01 to 5%, more preferably from 0.05 to 2%, based on the weight of the polymeric material of the layer.

The percentage of the thickness of the polyester base layer b) to the total thickness of the film is generally 40% to 90%, preferably 50% to 85%, or 60% to 80%.

The percentage of the thickness of the polyester base layer b) to the total thickness of the film is preferably higher than 50%, preferably higher than 60%, 65% or 70%.

The film for use according to the invention is preferably a three-layer structure comprising, in addition to the base layer b) and the first outer heat-sealable layer a), a third layer preferably directly adhered to the opposite side of the base layer b). Two outer polyester layers c).

The outer polyester layer c) of the film preferably comprises at least 80% by weight, preferably at least 85% by weight, at least 90% by weight of one or more polyesters, relative to the weight of the layer.

In one embodiment, layer c) consists of polyester.

The one or more polyester resins of layer c) may be the same or different from the resins of base layer b), preferably the same.

Preferably, the second outer polyester layer c) comprises an intrinsic viscosity, as measured according to ASTM D4603-03, of at least 0.75 dl/g or higher and/or a glass transition temperature Tg, as measured according to ASTM D3418, of not higher than 80°C and/or polyesters with melting points higher than 240°C.

Examples of suitable polyesters for outer layer c) are EASTAPAK 9921 from Eastman Chemical or RAMAPET N180 from Indorama Polyester.

The thickness of the outer layer c) is generally about 5% to 40% of the total thickness of the film, preferably 10% to 35%, more preferably 15% to 30%.

The thickness of the outer layer c) may be up to about 25 microns, preferably up to about 15 or 10 microns, more preferably about 0.5 to 10 microns, and more preferably about 0.5 to 7 microns.

The thickness of the two outer layers can be the same or different.

One or more layers of the films of the present invention may contain any of the additives conventionally used in the manufacture of polymeric films. Therefore, such as pigments, lubricants, antioxidants, radical scavengers, UV absorbers, heat stabilizers, anti-blocking agents, surfactants, slip agents, optical brighteners, gloss improvers, Reagents for viscosity modifiers.

In particular, to improve the processing of the film in high speed packaging equipment, slip agents and/or anti-blocking agents may be added to one or both outer layers. The additives may be added in the form of concentrates in polyester carrier resins. The amount of additives is generally on the order of 0.2% to 5% by weight of the total weight of the layer.

Where the package is not under vacuum, the film of the present invention preferably includes at least one surface having anti-fog properties. Typically, the anti-fog surface is the surface of the heat sealable layer directly facing the product.

To obtain an anti-fog surface, the anti-fog agent can be compounded directly into the polyester resin of the heat sealable layer prior to extrusion of the film used in the present invention. Suitable antifogging agents are, for example, nonionic fluorinated surfactants, such as fluorinated alkyl esters, perfluoroalkyl ethylene oxides, anionic fluorinated surfactants, such as quaternary ammonium salts of perfluoroalkyl sulfonates, Nonionic surfactants, such as polyol fatty acid esters, higher fatty acid amines, higher fatty acid amides, and ethylene oxide adducts of higher fatty acid amines or amides, etc. The amount of antifogging agent added to the heat-sealable layer is typically 0.5 to 8 wt %, 1 to 5 wt %, 1 to 3 wt % of the heat sealable layer.

Alternatively, the anti-fogging agent may be in the form of a coating applied to the heat-sealable outer layer. The antifogging agent can be applied to the heat-sealable layer using conventional techniques, such as gravure coating, reverse fit coating, fountain bar coating, or spray coating.

The application of the antifogging agent can be carried out by an in-line method including application during the manufacture of the polyester film, or by an off-line coating method including application after the production of the polyester film.

Suitable antifogging agents for such applications are nonionic surfactants such as polyol fatty acid esters, higher fatty acid amines, higher fatty acid amides, polyoxyethylene ethers of higher fatty alcohols and ethylene oxides of higher fatty acid amines or amides adduct. Among them, polyhydric alcohol fatty acid esters, polymethylene ethers of higher fatty alcohols, and glycerin fatty acid esters are preferable.

The amount of the antifogging agent coating is not particularly limited, but it may be 0.1 to 8 ml/m ² , 0.5 to 7 ml/m ² , 0.5 to 5 ml/m ² .

The thickness of the outer layer c) may be up to about 25 microns, preferably up to about 15 microns, more preferably 0.5 to 10 microns, and more preferably about 0.5 to 7 microns. The thickness of the two outer layers can be the same or different.

Films for use in the present invention may have any total thickness of 10 to 100 microns, 15 to 75 microns, more preferably 15 to 50 microns or 15 to 35 microns.

Preferably, the films of the present invention have a thickness prior to thermoforming of less than 50 microns, more preferably less than 40 microns, even more preferably less than 35, 30 or 25 microns.

Preferably, the film before thermoforming has a thickness greater than 10 microns, preferably greater than 12 microns, more preferably greater than 15 microns.

Preferably, the film before thermoforming has a thickness of 10 to 100 microns, preferably 15 to 75 microns, more preferably 15 to 50 microns or 15 to 35 microns.

Preferably, when the film is thermoformed in deep drawing, its total thickness prior to thermoforming is at least 15 microns, preferably 20 microns, more preferably 25 or 30 microns.

Preferably, the thickness of the film measured at the bottom of the thermoformed cavity after thermoforming is below 20 microns, preferably below 15 microns.

The polyester films used in the present invention are advantageous in that they provide comparable performance at lower thicknesses relative to dual bakeable thermoformable films currently on the market.

The polyester film used in the present invention may comprise a base layer b), a first outer heat sealable layer a) and a second outer layer c), wherein the second outer layer c) comprises the resin used in the base layer and the heat sealable layer Different polyester resins.

Alternatively, the polyester film may comprise a base layer b) and two outer heat sealable layers a) comprising the same amorphous polyester or the same crystalline polyester with a different melting temperature Above the melting temperature of the polyester of the base layer.

Alternatively, the polyester film may comprise a base layer b), a first outer heat sealable layer a) and a second outer layer c), wherein the second outer layer c) comprises the same polyester resin as the base layer b).

In one embodiment, the polyester film for use in the present invention comprises a base layer b) comprising a polyester having an intrinsic viscosity higher than 0.75 dl/g, a first outer heat sealable layer a) comprising an amorphous polyester, and a A second outer layer c) of the same polyester resin as the base layer.

In one embodiment, the polyester film for use in the present invention comprises a base layer b) comprising a polyester having an intrinsic viscosity higher than 0.75 dl/g, comprising a ternary blend of an amorphous polyester, a thermoplastic resin and a further polyester A first outer heat sealable layer a) of the material, and a second outer layer c) comprising the same polyester resin as the base layer.

Preferably, the polyester film comprises a base layer b) comprising at least 50%, 60%, 70%, 80%, 85%, 90%, 95% of a polyester having an IV above 0.75 dl/g Ester resin and not more than 50%, 40%, 30%, 20%, 15%, 10%, 5% amorphous polyester; first outer heat-sealable layer a), said first outer heat-sealable layer a) comprising amorphous polyester; and a second outer layer c) comprising the same polyester resin as the base layer. Preferably, the amorphous polyester in the base layer b) is the same as the amorphous polyester in the heat sealable layer a).

In one embodiment, polyester films for use in the present invention include:

- a heat sealable layer a) comprising

about 25 to 70% by weight of at least a first amorphous polyester having a melting temperature not higher than the melting temperature of the polyester of base layer b),

10 to 20% by weight of at least thermoplastic resin selected from polyamide, polystyrene, polyethylene, ionomer, ethylene/unsaturated carboxylic acid copolymer, ethylene/unsaturated ester copolymer, ethylene/propylene Copolymers, maleic anhydride modified polyethylene and ethylene/cyclic olefin copolymers, preferably maleic anhydride modified polyethylene, and

20 to 60% by weight of at least other polyesters characterized by an intrinsic viscosity of at least 0.75 dl/g or higher as measured according to ASTM D4603-03 and/or a glass transition temperature Tg of not greater than ASTM D3418 above 80°C and/or melting point above 240°C; and/or

- an inner polyester base layer b) comprising a mixture of at least 50% polyester resin with an IV higher than 0.75 dl/g and at most 50% amorphous polyester; and/or

- an outer polyester layer c) comprising an intrinsic viscosity of at least 0.75 dl/g or higher as measured according to ASTM D4603-03 and/or a glass transition temperature Tg of not higher than 80°C as measured according to ASTM D3418 and/or Or polyester with melting point higher than 240℃.

Preferably, the polyester film for use in the present invention consists of:

- a heat sealable layer a) comprising

about 25 to 70% by weight of at least a first amorphous polyester having a melting temperature not higher than the melting temperature of the polyester of base layer b),

10 to 20% by weight of at least thermoplastic resin selected from polyamide, polystyrene, polyethylene, ionomer, ethylene/unsaturated carboxylic acid copolymer, ethylene/unsaturated ester copolymer, ethylene/propylene Copolymers, maleic anhydride modified polyethylene and ethylene/cyclic olefin copolymers, preferably maleic anhydride modified polyethylene, and

20 to 60% by weight of at least other polyesters characterized by an intrinsic viscosity of at least 0.75 dl/g or higher as measured according to ASTM D4603-03 and/or a glass transition temperature Tg of not greater than ASTM D3418 above 80°C and/or melting point above 240°C; and

- an inner polyester base layer b) comprising a mixture of at least 50% polyester resin with an IV higher than 0.75 dl/g and at most 50% amorphous polyester; and

- an outer polyester layer c) comprising an intrinsic viscosity of at least 0.75 dl/g or higher as measured according to ASTM D4603-03 and/or a glass transition temperature Tg of not higher than 80°C as measured according to ASTM D3418 and/or Or polyester with melting point higher than 240℃.

In one embodiment, the polyester film for use in the present invention consists of:

- a heat sealable layer a) consisting of:

about 40 to 70% by weight of at least a first amorphous polyester having a melting temperature not higher than the melting temperature of the polyester of base layer b),

10 to 20% by weight of at least a thermoplastic resin selected from the group consisting of ethylene/unsaturated carboxylic acid copolymers, ethylene/unsaturated ester copolymers and maleic anhydride modified polyethylene, and

20 to 50% by weight of at least other polyesters characterized by an intrinsic viscosity of at least 0.75 dl/g or higher and/or a glass transition temperature Tg not higher than 80°C and/or a melting point higher than 240°C ;and

- an inner polyester base layer b) consisting of a mixture of at least 55% polyester resin with an IV above 0.75 dl/g and at most 45% amorphous polyester; and

- an outer polyester layer c) comprising at least 95% of the same polyester as the base layer b), said polyester being characterized by an intrinsic viscosity of at least 0.75 dl/g.

Preferred membranes for the use of the present invention are those consisting of:

- an outer heat sealable layer a) consisting of about 60% by weight of PETG, 25% by weight of PET and 15% by weight of modified LLDPE or EAA;

- an inner base layer b) consisting of about 60% by weight of PET with an IV above 0.75 dl/g and 40% by weight of PETG; and

- An outer polyester layer c) consisting of about 98% by weight of the same PET as the base layer and 2% by weight of PETG.

Exemplary membranes useful in the present invention and methods for their manufacture are described in WO2012160142 and WO2007093495.

Other possible membranes and their preparation are disclosed in WO2009013284 (eg, the membrane of Example 2) and WO2013080143 in the name of Cryovac.

The Applicant has surprisingly found that the above polyester films exhibit such good formability and shrinkability that they can be advantageously used in deep drawing and/or thermoforming-shrinking applications. In a preferred embodiment, the film is used in a deep draw thermoforming-shrink wrapping process.

The formability of polyester films used in the method of the present invention can be assessed visually after a thermoforming cycle, by calculating the thermoforming draw ratio or preferably by measuring the actual volume of the thermoforming cavity.

The thermoforming draw ratio represents a theoretical value for formability and is calculated based on the die size as follows:

Draw ratio = surface area of the mold/footprint of the mold.

An example of calculating the draw ratio for a 2 cm deep parallelepiped mold is as follows:

Mold size: 10 cm long x 12 cm wide x 2 cm deep

Surface Area: 2(10 cm x 2 cm) + 2(12 cm x 2 cm) + (10 cm x 12 cm) = 208 cm ²

Footprint: 10 cm x 12 cm= 120 cm ²

Stretch ratio: = 1.7

The stretch ratio represents the maximum stretch that the material can experience in the mold if it conforms to the mold ideally.

Preferably, in the deep drawing method of the present invention, the draw ratio in the forming step is higher than 2.0, more preferably higher than 2.5, 3.0, 3.5, 4.0 or 4.5.

However, depending on the formability of the film and the mold configuration, the actual stretch ratio (ie, the stretch ratio evaluated on the thermoformed container) may even differ significantly from the theoretical value.

The actual stretch ratio can be difficult to calculate, especially in the case of irregularly shaped or ribbed containers.

By comparing the actual volume of the thermoformed cavity of the container to the volume of the mold, the evaluation of the formability of the film can be more easily performed. These volumes can be estimated indirectly based on the weight of water required to fill the cavity or mould, respectively, as explained in this experimental section under "Volume test" (shrinkage index after thermoforming).

The difference in the volume (or water weight) of the cavity and the mold is related to the formability of the tested material.

This volume difference can be calculated as explained later according to the following formula:

ΔV%= [(V cavity-V mold)/V mold] x 100= [(Ww cavity-Ww mold)/Ww mold] x 100

where V is the volume of the cavity or mould (eg in cc) and Ww is the weight of water filled in the cavity or mould in grams. The more negative the percentage, the more the film retracts after removal from the mold.

The polyester films used in the thermoforming process of the present invention are characterized by a difference in volume percentages typically below -35%, preferably below -30% or below -25%, which means that the actual volume of the thermoformed cavity is very close The original volume of the mold. For the commercial comparative film Mylar tested in this experimental section, this difference is generally quite significant, i.e. above -35%, eg -40% or more, which means that even when thermoformed at the same stretch ratio, the commercial film is Less formable, and produced cavities of significantly smaller volume (see pictures of Figures 2A-2C).

Films used as bottom webs according to the present invention may or may not be heat shrinkable.

In one embodiment of the deep draw packaging method, the polyester film may be non-heat shrinkable, ie, the percent free shrinkage in both the LD and TD directions is less than 3%, preferably less than 2%.

In this case, after orientation, the polyester film is heat set by a custom annealing step.

Preferably, the polyester film used in the deep drawn food packaging method may be heat shrinkable. Advantageously, the films of the present invention are imparted with very good shrink properties even after thermoforming, thereby providing a very tight and attractive package for final heating.

In thermoform-shrink applications, polyester films are heat shrinkable both before and after thermoforming.

In a preferred embodiment of the thermoforming-shrink packaging method of the present invention, the polyester film of the bottom web is heat shrinkable, it is formed at a draw ratio higher than 1.26, and the sealed package is finally heat shrinkable.

Preferably, the polyester film used for thermoforming-shrink packaging has a free shrink percentage of at least 3%, more preferably at least 4%, in at least one of the LD or TD directions prior to thermoforming. Preferably, the polyester film has a percent free shrinkage in both the LD and TD directions of at least 3%, more preferably at least 4%, before thermoforming, as measured by the test method described in this experimental section.

Preferably, the polyester film has a total free shrinkage percentage before thermoforming of at least 5%, more preferably at least 10%, as measured according to the test method described in this experimental section.

Advantageously, polyester films used in thermoforming-shrinking processes exhibit significant shrinkage properties after thermoforming, thus allowing tight shrinkage around the product and improved appearance of the package without wrinkles after gentle heating such as in an air shrink tunnel or vacant gas.

In particular, the polyester films used in the thermoformed-shrinkable food packaging of the present invention have a percent free shrinkage of at least 15%, more preferably at least 20%, in at least one of the LD or TD directions after thermoforming.

The polyester film used in the thermoforming-shrink food packaging method of the present invention exhibits a free shrink percentage of at least 15%, more preferably at least 20%, even more preferably at least 23% in both the LD and TD directions after thermoforming.

The polyester film used in the thermoforming-shrink food packaging method of the present invention exhibits a total free shrinkage percentage after thermoforming of at least 40%, preferably at least 43%, more preferably at least 45% or 50%.

A preferred feature of the polyester film used in the packaging method of the present invention is a tensile strength in at least one of the LD or TD directions, measured at 23°C (ASTM D882), of at least 1500 Kg/cm ² , more preferably at least 1600 Kg/cm ² .

A preferred feature of the polyester film used in the packaging method of the present invention is that the tensile strength in both the LD and TD directions measured at 23°C (ASTM D882) is at least 1500 Kg/cm ² , more preferably at least 1600 Kg /cm ² .

A preferred feature of the polyester film used in the packaging method of the present invention is an elongation at break in at least one of the LD or TD directions, measured at 23°C (ASTM D882), of at least 100%, more preferably at least 105%.

A preferred feature of the polyester film used in the packaging method of the present invention is that the elongation at break in both the LD and TD directions, measured at 23°C (ASTM D882), is at least 100%, more preferably at least 105%.

The polyester film used in the packaging method of the present invention is preferably characterized by an elastic modulus in at least one of the LD or TD directions, measured at 23°C (ASTM D882), of at least 20,000 Kg/cm ² , more preferably at least 22,000 Kg/cm ² .

A preferred feature of the polyester film used in the packaging method of the present invention is an elastic modulus of at least 20,000 Kg/cm ² , more preferably at least 22,000 Kg, measured at 23° C. (ASTM D882) in both the LD and TD directions /cm ² .

The polyester films used for the purposes of the present invention are dual bakeable, so that thermoformed containers and packages made therefrom can withstand reheating in a microwave or conventional oven and in conventional ovens at temperatures above 205°C and Packaged cooking at very high temperatures up to 220°C.

Films of the present invention with peelable sealants provide easy-to-open packaging. In addition, the films of the present invention provide a self-venting package, ie a package that opens at the seal and releases internal vapors during cooking.

Due to the polyester-based composition, the films of the present invention provide final packaging with excellent optical properties (transparency and gloss).

The polyester film used in the present invention can be produced according to any method known in the production technology of a biaxially oriented film, for example, a tubular or flat film orientation method.

Polyester films, preferably three-layer films, can be prepared by coextrusion, by coating or by extrusion coating, preferably by coextrusion according to the tubular process or the flat process.

In the tubular process, also known as the "double-bubble" process, simultaneous biaxial orientation is obtained by extruding a thermoplastic resin tube, which is subsequently quenched, reheated, and then expanded by internal air pressure to induce transverse orientation, and to induce longitudinal orientation Orientation rate winding. An example of a device suitable for the technique is disclosed in US4841605.

In the flat film method, a film-forming thermoplastic resin is extruded through a T-die and rapidly quenched on chill rolls to ensure that the resin is quenched to an amorphous state. Orientation is then achieved by simultaneously or sequentially, preferably simultaneously, stretching the quenched extrudates at a temperature above the glass transition temperature of the thermoplastic resin.

In a continuous flat orientation process, the flat quenched extrudate is first oriented in one direction, usually the machine direction, ie, the advancing direction through the film stretcher, and then in the transverse direction. The longitudinal stretching of the extrudate is conveniently carried out on a set of rotating rolls (MDO) rotating at different speeds. At least one of the first pair of rolls is heated, for example by internal circulation of hot oil. The transverse stretching is usually carried out in a tenter frame apparatus (TDO) which includes a certain number of heating means and suitable stretching means.

In simultaneous flat orientation, the resulting hot and sheared sheet is directed to the stretching zone of a simultaneous tenter. Any simultaneous stretching device can be used in the zone. Preferably, however, the gripper is advanced over the entire opposing ring of the tenter frame by means of a linear synchronous motor. Bruckner GmbH has designed a suitable line for simultaneous stretching with linear motor technology and is advertised as a LISIM line. An alternative line for simultaneous stretching of extruded flat belts is a pantograph-based DMT line equipped with two separate monorails on each side of the orientation unit. The configuration of the tenter frame can vary depending on the desired draw ratio. In a subsequent annealing step, the biaxially oriented film can be dimensionally stabilized by heat treatment at a temperature below the melting temperature of the film.

Preferably, the polyester films used in the present invention are produced according to flat coextrusion. The polymer for the base layer b), the polymer for the heat-sealable outer layer a) and the polymer for the second outer layer c) are fed into separate extruders. The melt was extruded through a multilayer T-die and quenched on chill rolls. The casting thus formed is then biaxially oriented, preferably simultaneously.

In the case of sequential orientation, the longitudinal stretching (LD or machine direction orientation) of the extrudate is suitably carried out at a temperature in the range of 60 to 120°C, preferably 70 to 100°C, and the transverse stretching (lateral orientation) at 90°C It is performed in the range of ℃ (preheating zone) to 130°C (stretching zone), preferably 90°C (preheating zone) to 110°C (stretching zone). The longitudinal stretch ratio is in the range of 2.0:1 to 5.0:1, preferably in the range of 2.3:1 to 4.8:1. The transverse stretch ratio is generally in the range of 2.4:1 to 6.0:1, preferably in the range of 2.6:1 to 5.5:1.

Preferably, however, the polyester films used in the present invention are simultaneously oriented.

The temperatures for simultaneous orientation are 90 to 110°C (preheating zone) and 90 to 110°C (stretching zone), respectively, preferably 90 to 100°C and 93 to 103°C, respectively.

The LD draw ratio is 2.5:1 to 5:1, preferably 3.0:1 to 4.2:1, and the TD draw ratio is 2.5:1 to 6:1, preferably 3.2:1 to 4.4:1.

The annealing is carried out at a temperature of 160 to 250°C, preferably 180 to 240°C, even more preferably 220 to 240°C. Annealing temperature can be used to fine-tune the final shrinkage properties of the film.

Preferably, the polyester films used according to the invention are biaxially oriented and heat set.

Preferably, the deep thermoformed polyester films used in the present invention have a percent free shrinkage in both LD and TD of less than 10% (measured within 5 minutes in an oven at 180°C as described in the experimental section).

Preferably, the deep thermoformed biaxially oriented polyester film used in the present invention is heat set to a total free shrinkage percentage below 15%, preferably below 10% or 5%.

Preferably, the shrink-thermoformed biaxially oriented film used in the present invention has a total free shrinkage percentage before thermoforming of at least 5%, as measured in an oven at 180°C, according to the test method reported in the experimental section, and more Preferably at least 10%.

The bi-oriented polyester film is finally cooled and wound up in a conventional manner.

Other methods of making the films of the present invention include applying the heat sealable polymer of layer a) to a substrate layer comprising layers b) and c). Coating can be carried out using any suitable coating technique, including gravure roll coating, reverse roll coating, dip coating, bead coating, extrusion coating, melt coating, or electrostatic spraying. Coating can be performed "offline", ie, as a separate step after the stretching and subsequent heat setting of the base layer, or "inline", ie, before, during, or between any stretching operations.

Before applying the heat sealable layer to the substrate, if desired, the exposed surface of the substrate can be subjected to chemical or physical surface modification treatments to improve the bond between the surface and the subsequently applied layer. For example, exposed surfaces may experience high voltage electrical stress associated with corona discharge. Alternatively, solvents or swelling agents known in the art can be used, such as halogenated phenols dissolved in common organic solvents, eg, p-chloro-m-cresol, 2,4-dichlorophenol, 2,4,5- Or a solution of 2,4,6-trichlorophenol or 4-chlororesorcinol in acetone or methanol to pretreat exposed surfaces.

The polyester film used in the present invention can be printed. Printing materials prior to thermoforming improves consumer appeal.

In view of use, the top and bottom webs are preferably approved by the relevant authorities for food applications.

The method according to the present invention comprises the following steps:

- providing the previously described thermoformable bibakeable biaxially oriented polyester film as the bottom web;

- forming the bottom web so as to provide at least a cavity with openings;

- placing food product in said cavity through said opening;

- at the opening, preferably under vacuum, by hermetically sealing the bottom web itself or by providing a dual-bakeable top web and wrapping the dual-bakeable top web around the opening the top web is hermetically sealed to the bottom web to close the cavity; and

- Cut out the sealed package.

The thermoformed food packaging method of the present invention is characterized in that

-i) in the forming step, the draw ratio is higher than 1.26 (deep-drawn food packaging method), preferably higher than 2, higher than 3, higher than 4 or even higher than 4.5, thereby providing a deep-drawn thermoformed packaging, or

-ii) Use of a heat shrinkable film and a further final shrinking step after thermoforming (thermoforming-shrink food packaging method) to provide a thermoforming-shrink packaging.

Preferably, the thermoformed food packaging method of the present invention is characterized in that

-i) in the forming step, the draw ratio is higher than 1.26 (deep drawing food packaging method), and

-ii) Use of a heat shrinkable film and a further final shrinking step after thermoforming (thermoforming-shrink food packaging method) to provide deep drawn thermoforming-shrink packaging.

Preferably, the thermoformed cavity ends have a peripheral heat sealable flange around the opening.

If a top web is present, the top web can be any dual bakeable film suitable for hermetically closing the openings of thermoformed cavities in the bottom web.

The top web may be shrinkable or non-shrinkable, thermoformable or non-thermoformable, with the same or a different, generally smaller thickness than the bottom web, depending on the final packaging variant desired.

The top web can be a flat film, another thermoformed flexible container (commonly used to package protruding products), or a stretch film.

In one embodiment, the top web is a different film than the bottom web.

The dual bakeable top web may be a single layer film, preferably based on polyester, or in the alternative may be a multi-layer film comprising a substrate preferably based on polyester and a heat sealable layer. The heat sealable layer participates in bond formation with the bottom web to provide the final airtight package.

Since the bottom web includes a heat seal layer, the top web may or may not include a heat seal layer.

In one embodiment, the top web has the same composition as the bottom web.

In one embodiment, the top web has the same composition and thickness as the bottom web.

In one embodiment, the top web has the same composition, thickness and shrinkage properties as the bottom web.

In one embodiment, the top web is the same film as the bottom web.

The total thickness of the top web is typically 12 to 200 microns, preferably 12 to 100 microns, more preferably 15 to 35 microns.

The forming step of the packaging method of the present invention is the step of forming at least one cavity in the bottom web, preferably surrounded by a flat peripheral portion, ie a flange.

The forming step is carried out by thermoforming, preferably vacuum thermoforming, possibly plunger assisted thermoforming, according to conventional techniques and using commercially available equipment.

"Thermoforming" refers to a method comprising the steps of heating a material to a temperature (T1), wherein T1 is above the glass transition temperature (Tg) of the material, and if the material exhibits a crystalline melting temperature (Tm), Where T1 is below the crystalline melting temperature, the material is then subjected to deformation, ie the material is deformed while it is in its softened rubbery solid state.

In one embodiment, the packaging method of the present invention is carried out at higher draw ratios (deep draw) without any final shrinkage of the packaging.

In the deep drawn food packaging method, the draw ratio in the forming step is preferably higher than 2.0, higher than 2.5, higher than 3.0, higher than 3.5, higher than 4.0 or even higher than 4.5.

The deep drawing method provides a great deal of freedom in the shape and size of the container. The films of the present invention allow for smoothing and deep drawing, thereby providing containers with uniform thickness, large internal volume, and high mold engraving definition.

The step of closing the cavity requires heat sealing the top web to the bottom web around the opening, preferably along a dedicated flat surface, ie along the peripheral flange, or self-sealing the bottom web at the cavity opening.

For effective heat sealing, the polymeric material of at least one heat-sealable surface should soften enough to adhere to the other surface to be sealed.

Typically, the heat sealing properties of a polyester layer having a melting temperature (Tm) are manifested at temperatures below Tm, and in this case it is not necessary to exceed Tm when forming a heat seal bond.

Exemplary heat seal temperatures for the top and bottom webs of the present invention are 190°C to 220°C.

In another embodiment, the packaging method of the present invention is a thermoforming-shrink packaging method wherein at least the bottom web is heat shrinkable, and optionally both the top and bottom webs are heat shrinkable.

The heat shrinkage of the packaging material of the bottom web or both the bottom and top webs caused by the heat treatment provides the desired tight appearance for the final preferred vacuum packaging.

The polyester film used as the bottom web in the thermoforming-shrink food packaging method of the present invention has a very high shrinkage rate after thermoforming, thus providing a very tight dual bakeable, Vacuum packaging is preferred.

There are several variations of the thermoforming shrink packaging method of the present invention, such as the use of lids, which may or may not be heat shrinkable, may or may not be deep drawn, or may or may not be in-product stretched.

Furthermore, there are different ways to shrink the package, such as heating only the deep-drawn container or the entire package, performing a heat shrink step on the final package leaving the sealed, preferably vacuum chamber, or the package still in the vacuum chamber before or after the package is sealed heat shrinking step.

The constriction is preferably performed using an air constriction channel outside the seal, preferably outside the vacuum chamber, preferably after sealing.

In Figure 3, a "thermoform-shrink" packaging process is schematically shown. The film, indicated at 1, is in the form of a web blank unwound from a roll and clamped transversely by endless chains (not shown in the figures) and directed from the line entry to the deep drawing station F. In this station, the heat softened thermoplastic film is deep drawn in the die 100 once the heating plate 101 has heated the film to a temperature sufficient to soften it. Heating can be accomplished by radiation (eg, infrared radiation), convection, conduction, or any combination of these methods. The temperature reached by the film should be high enough to allow it to form well, but not so high that the film may flow excessively. Typically, in the thermoforming method of the present invention, a temperature of about 180-200°C is used. In the basic forming method, the main force that brings the softened plastic film into contact with the mold is the pressure difference between the two sides of the plastic sheet. This can be done by applying a vacuum in the mould through ports (in the bottom of the mould, not shown) and/or by having compressed air from a port (in the plate above the mould, not shown) forcing the softened plastic into contact with the mould accomplish. Other methods, such as plug-assisted thermoforming methods, may be used in the forming step, but for films like the films of the present invention, it appears that these more complex methods need not be used. The mold can be a single cavity or multi-cavity mold, and the shape of each cavity can be changed as desired. It is preferred to use a mold with a depth of about 40 to about 140 mm. Once the forming step in station F has been completed, the mould 100 is lowered and the forming containers 2, still joined together by the laterally clamped plastic web, are guided along the packaging line to the loading station G, where At position G, they are loaded manually or automatically with the product 3 to be packaged. The loaded container is then moved to a vacuum sealed chamber H where the upper film 4 is supplied on top of the loaded container 5 . The vacuum sealed chamber H is made of a lower part 102 and an upper part 103 which can be moved in a reciprocating manner in the direction of the arrow to close the chamber. Once the chamber is closed, the space within the chamber, including the space between the loaded deep draw container 5 and the upper film 4, is evacuated, and then the sealing frame (not shown in Figure 3) is actuated to follow the convexity of the deep draw container The rim seals both. If the product loaded into the deep drawn container protrudes above the plane of the container flange, the upper film 4 will necessarily be deep drawn like the lower film, or stretched on the top surface of the product. In both cases, the upper membrane will have to be gripped laterally by the multi-strand endless chain. In the former case, a forming station as described above but providing an inverted deep drawing of the container would exist upstream of the vacuum sealing station H to deep draw the upper lidding film. The mould used in this case will have the same shape as the mould used for the lower film, but not necessarily the same depth, and the deep-drawn container 3 and the deep-drawn lid obtained from the upper film 4 will enter the vacuum sealing station H , so that once the chamber is evacuated, its flanges will overlap. In the latter case, the clamped upper film is heated enough to allow it to stretch easily before it is directed into the vacuum-sealed chamber. Heating can be accomplished by contacting the membrane with the heating plate 104 or by any other known means.

Once the package is sealed in the vacuum sealed chamber H, air is returned to the chamber and the chamber is opened. The packages 6(I) are separated inside or outside the vacuum chamber by means such as cutters and then transferred to the shrinking station L, where they are subjected to a heat treatment which shrinks the packaging material and gives the final package 7 a tight fit. Exterior. For example, a water bath, a hot air channel or an IR heater may be suitably employed in said steps.

In one embodiment, the packaging method of the present invention includes deep drawing of the bottom web and final shrinkage of the closed package.

The deep drawing thermoforming-shrink wrapping method can be summarized as including the following steps:

1. Heating a bi-bakeable biaxially oriented heat-shrinkable bottom web (polyester film of the invention as previously described) and forming it in a mold with the aid of positive or negative pressure such that the bottom The web is deeply formed in the shape of a deep die.

2. Place the food product in the forming cavity of the bottom web.

3. Preferably, vacuum is applied and the top web is heat sealed to the opening of the cavity in the bottom web so that the package is completely sealed.

4. Heat shrink the whole package for better and more attractive appearance.

In the thermoforming-shrink wrapping method of the present invention, the dual bakeable biaxially oriented film is heat shrinkable and is characterized by at least LD or TD measured as described in the experimental section prior to thermoforming The % free shrinkage on one is at least 3%, preferably at least 4%.

In the thermoforming-shrink wrapping method of the present invention, the dual bakeable biaxially oriented film after thermoforming is characterized by a total percent free shrinkage measured as described in the experimental section after thermoforming of at least 40%, preferably At least 43%, more preferably at least 45% or 50%.

A second object according to the present invention is a dual bakeable thermoformable flexible container comprising a thermoformed cavity and an opening, made by thermoforming a film of the bottom web as described above, wherein the thermoformed cavity is The depth is greater than 1 cm and/or the thermoformed container is heat shrinkable.

The flexible container according to the present invention has a stretch ratio higher than 1.26, preferably higher than 2.0, more preferably higher than 2.5, even more preferably higher than 3.

Preferably, the depth of the thermoformed cavity is higher than 2 cm, more preferably higher than 3 cm, or 4 cm, or 5 cm, or 6 cm, or 7 cm, or 8 cm, or 9 cm, or 10 cm.

Preferably, the thermoformed container of the present invention is heat shrinkable. In particular, the thermoformed film of the container has a total free shrinkage percentage measured as described in the experimental section after thermoforming of at least 40%, preferably at least 43%, more preferably at least 45% or 50%.

Preferably, the container of the present invention is both deep drawn, ie thermoformed at a depth above 3 cm, or 4 cm, or 5 cm, or 6 cm, or 7 cm, or 8 cm, or 9 cm, or 10 cm, Also heat shrinkable, ie having a total free shrinkage percentage after thermoforming of at least 40%, preferably at least 43%, more preferably at least 45% or 50%.

Preferably, the container includes a cavity, an opening, and a flat surface (ie, a flange) surrounding the opening, onto which the top web can then be sealed, thereby providing an airtight flexible package.

As can be seen from the deep drawing tests described in Example 1, the thermoformed container according to the invention is characterized by a uniform thickness of the thermoformed film along the bottom and in particular along the walls, which cannot be obtained with the comparative prior film Mylar . This uniform distribution of material after thermoforming is attributed to the high formability of the films used to make the containers of the present invention.

Preferably, in the container of the present invention, after thermoforming, the thickness of the film measured at the bottom of the container is less than 25 microns, more preferably less than 20 microns, even more preferably less than 15 microns.

In one embodiment, the thermoformed container may be prepared by thermoforming a composite comprising a polyester film as previously described, which is adhered as a liner by conventional techniques such as by glue lamination or thermal lamination Attached to cardboard.

Figure 1 shows a cross section of a deep drawn thermoformed container (201) according to the present invention. The container (201) may be part of a semi-finished web comprising a plurality of thermoformed containers (201). Each container (201) includes a drawn portion forming a cavity (202) defined by a bottom (202a), side walls (202b) extending from the bottom and a top opening (203) (see Figure 1 ). dashed line).

The top opening 203 is surrounded by a flat peripheral portion 204 (ie, a flange). The top opening (203) forms an inlet mouth through which the food product to be packaged is introduced during the packaging process. When viewed from the top, opening (203) may assume any convenient shape, such as rectangular, square, circular, oval, or other shape suitable for allowing product to enter cavity (202). The container (201) is characterized by a height H, a length L and a width W.

As previously mentioned, the actual stretch ratio can be calculated based on measurements (H, L and W) of the cavity of the thermoformed container.

The difference between the calculated stretch ratio for the mold and the actual stretch ratio calculated for the thermoformed container can provide an index of the actual formability of the film. However, the evaluation is difficult if the thermoformed container has an irregular shape or does not have a flat surface.

As explained in detail in the experimental section, a simpler formability index ( shrinkage index after thermoforming ) can be calculated indirectly from the thermoformed cavity of the container and the volume of the mold, by weighing the water required to fill said volume to evaluate.

Preferably, the polyester film used in the method of the present invention and the containers made therefrom have a shrinkage index after thermoforming, measured as described in this experimental section, below -35%, more preferably below -30%, even more Preferably below -25% or -20%.

Advantageously, the thermoformed container of the present invention is then used to package an article (foodstuff), preferably vacuum sealed, and preferably shrunk to provide a tight package.

A third object according to the present invention is a dual bakeable airtight thermoformed package comprising

A dual bakeable thermoformable flexible container as previously described comprising a thermoformed cavity and an opening,

food placed in said cavity,

The opening is hermetically closed by a flexible container that is self-sealing at the opening or by a dual bakeable top web sealed around the opening to the container.

In one embodiment, the package according to the present invention does not include a top web, but only a flexible container that self-seals at the opening of the cavity, thereby enclosing the product.

Preferably, the package according to the present invention comprises a top web sealed around the opening of the container.

With regard to possible variants of the packaging according to the invention, the same possibilities reported for the packaging method are applied here, namely the presence or absence of a top web, a flat, stretched or stretched top web, heat-set Or heat shrinkable top web etc.

In a thermoformed package according to the invention, preferably a deep drawn and/or shrink package, at least the container according to the invention is thermoformed.

In this case, the opening of the container may be closed by a non-thermoformable lid, which may be made of the same film of the container or a different dual bakeable film.

In one embodiment, the non-thermoformed lid and thermoformed container are made from the same films described above. Preferably, the film of the lid is thinner than the film of the container.

In another embodiment, both the top and bottom of the package may be thermoformed at the same or different depths, but at least one of them is deep drawn.

Preferably, the packaging of the present invention is evacuated.

Preferably, the package of the present invention is evacuated and heat shrunk.

Thermoformed packages are typically obtained on thermoformers using roll stock material. Two rolls are used, one for the bottom web which is unwound, heated by a hot plate and forms a cavity in which the product to be packaged is then loaded and one roll for the top The web, if present, is sealed to the bottom web inside a sealed vacuum chamber that has preferably been de-aired.

In one embodiment of the package of the present invention, the bottom is thermoformed to provide a cavity and a surrounding flange, and the top is sealed around the flange. The thermoformed bottom may be prefabricated or thermoformed in-line, preferably it is thermoformed in-line.

In one embodiment of the package of the present invention, the package comprises two separate pieces of film: a top and a bottom, sealed together along the peripheral surface around the product. In said embodiment, the bottom is thermoformed so as to provide a cavity, the top and bottom films are both dual bakeable films, preferably the top and bottom films, substantially made of polyester as defined above are the same film, more preferably both are heat shrinkable.

In the packaging of the present invention, the product is a food product, preferably selected from fish (whole or in small portions), meat, especially fresh red meat, processed meat, poultry, pork, lamb, baked goods (also partially baked or frozen) ), seafood, stabilized vegetables or ready-to-eat meals.

Optionally, the packaged food product can be frozen for longer storage, and then the same package can be placed directly in the oven for cooking.

In a preferred embodiment, the package according to the invention is self-venting, ie it allows excess steam to escape the package during cooking. Advantageously, during cooking, the packaging of the present invention is restricted from opening along the seal, thus preserving some juices, and thus providing a well-cooked food that is tasty, tender and juicy inside and toasted on the surface.

Therefore, the fourth object of the present invention is a method for cooking food comprising

- providing a dual bakeable thermoformable package according to the invention comprising said product, and

- Cooking the packaged food in the package in a microwave or conventional oven.

In one embodiment of the method, the cooking step is performed in a conventional oven at a temperature above 205°C and/or at most 220°C.

Example

The invention can be further understood by reference to the following examples, which are illustrative only and should not be construed as limiting the scope of the invention, which is defined by the appended claims.

The films used in the method of the present invention comprise the following resins:

PET1 : RAMAPET N180, Indorama polyester, copolymer of terephthalic acid, isophthalic acid and monoethylene glycol, density 1.4 g/cc, intrinsic viscosity 0.80 dl/g, glass transition temperature 78°C, melting point 245°C .

PET2 : Copolyester Eastman Chemical EASTAPAK 9921, density 1.4 g/cc, melting point 238.0°C, intrinsic viscosity 0.80 dl/g.

PETG1 : Copolyester of terephthalic acid, 1,4-cyclohexanedimethanol and ethylene glycol, EASTAR PETG 6763-Eastman Chemical, polyethylene terephthalate/glycol, density 1.27 g/cc, Glass transition temperature 81°C, melt flow rate (Cond. 200°C/05.00 kg (G)) 2.8 g/10 min, viscous solution 0.75 mPa.sec.

PETG2 : Anti-blocking and slippage masterbatch of amorphous polyethylene terephthalate/glycol, copolyester of terephthalic acid, 1,4-cyclohexanedimethanol and ethylene glycol, SUKANO G dc S503 silica 10%, wax 6%, bulk (apparent) density 1.2 g/cc, Vicat softening point 82 ℃.

Modified LLDPE : BYNEL 4104 (2006) DuPont, maleic anhydride modified ethylene/butene copolymer, density 0.9200 g/cc, melt flow rate (Cond. 190℃/02.16 kg(E)) 1.10 g/10 min, melting point 125°C.

EAA : PRIMACOR 3440 Dow ethylene/acrylic acid copolymer, comonomer content acrylic acid 9.7%, density 0.938 g/cc, melt flow rate 190 ℃/02.16 kg 10 g/10 min, Vicat softening point 76 ℃.

In Tables 1 and 2 below, the compositions (% by weight relative to layer weight) of films 1 to 9 for the thermoforming method according to the invention are shown:

Table 1

Table 2

Films 1 to 9 were produced in a tenter LISIM® line according to the following methods and conditions.

The three layers were coextruded through a three-layer feedblock and then distributed through a flat die with a multi-manifold system. The melt from the die was quenched onto the chill roll; electrostatic pinning was used to facilitate intimate contact between the melt and chill roll. The casting thus formed is then biaxially oriented.

Stretching was performed simultaneously at an orientation ratio of 3.6:1 in MD and 3.8:1 in TD, and at temperatures of 95°C (preheating zone) and 98°C (stretching zone). The films were annealed at a temperature of 230°C to 235°C before leaving the oven. Finally the bi-oriented film is cooled, edge trimmed and wound into a mill log.

Comparative film

Mylar® OL is a dual process bakeable biaxially oriented polyester film with an amorphous polyester heat seal layer, manufactured by DuPont Teijin, commercially available in nominal thicknesses of 50, 75, 100 and 150 microns . There is no information on the polyester of the base layer.

Mylar CKP5E is an uncoated formable polyester film designed by DuPont Teijin for shallow draw thermoformable double bakeable packaging, also known as Mylar® COOK, which is designed for thermoforming on most roll materials equipment. Polyester is defined as a polyethylene terephthalate polymer.

testing method

Films used in the thermoforming process of the present invention and commercial comparative films were evaluated using the following test methods:

Free Shrinkage % : Evaluations were performed both before and after thermoforming, as explained below.

% Free Shrinkage Before Thermoforming : 12 cm x 12 cm square samples were cut from the tested films. On the surface of each sample, draw a 10 cm x 10 cm central square with a pencil.

The samples were placed in a laboratory oven at 180°C for 5 minutes in air without restriction. The dimensional change in both the LD and TD directions of the delineated squares for each sample was measured.

For each of the LD and TD directions, calculate the percent free shrinkage with the following formula

[(Lo -Lf)/Lo] x 100

where Lo is the initial length (mm) of the film sample before testing, and Lf is the length (mm) of the film sample after shrinkage.

Total % Free Shrink : It is the sum of the % Free Shrink in LD and TD of the film sample measured as described above.

% Free Shrinkage After Thermoforming : Cut a 7 cm x 7 cm square sample from the bottom of the thermoformed material under test. On the surface of each sample, use a pencil to outline a 5 cm x 5 cm central square.

The samples were placed in a laboratory oven at 180°C for 5 minutes in air without restriction. The dimensional change of the delineated squares for each sample was measured in both the LD and TD directions.

For each of the LD and TD directions, calculate the percent free shrinkage with the following formula

[(Lo -Lf)/Lo] x 100

where Lo is the initial length (mm) of the film sample before testing, and Lf is the length (mm) of the film sample after shrinkage.

Maximum Shrink Tension : That is, the force per original unit width produced by a film in the machine direction (LD) or transverse direction (TD) at a specified temperature as the film attempts to shrink (while under restraint), by the following internal test method Measurement: Cut 25.4 mm wide strips from the sample in either the longitudinal or transverse direction. The force measurement is carried out by means of a load cell to which the clamping jaws are attached. Opposite the clamping jaw, a second clamping jaw on which the sample is held is adjusted into position by means of an external handle to pretension the sample. Two clamping jaws hold the sample in the center of the channel, into which the impeller blows hot air. Three thermocouples were fixed in the air channel to measure the temperature. The temperature of the sample, as measured by the thermocouple, was raised to about 180°C at a rate of about 2°C/sec, and the force was measured continuously. The measured force was then divided by the original width of the sample to obtain the shrinkage force, and further divided by the thickness of the film sample to obtain the shrinkage tension. Typically, shrinkage tension is expressed in kg/cm ² .

Elastic Modulus: (23℃) ASTM D882

Tensile Strength and Elongation at Break: (23℃) ASTM D882

Haze : ASTM D1003

Gloss: ASTM D2457 (60°)

Tg and Melting Point: ASTM D3418

Formability : Evaluate film formability by visual inspection, looking for defects in material conforming to mold shape and details, by measuring material thickness in different parts of the thermoformed container, and by assessing the volume of the cavity according to the volume test described below sex.

Volume test (shrinkage index after thermoforming)

The purpose of this very simple test is to evaluate the formability of a film and its shrinkage after thermoforming by measuring the actual volume of the cavity of a container made from the film by thermoforming under specific conditions. The volume of the cavity of the thermoformed container was indirectly evaluated by measuring the weight of water required to fill the thermoformed cavity up to the flange. The higher the weight of the water, the greater the volume of the cavity and, therefore, the more formable the membrane is.

Therefore, considering a water density of 1 g/cc, the volume difference between the thermoforming cavity and the mold in percent can be calculated as follows:

ΔV%= [(V cavity-V mold)/V mold] x 100= [(Ww cavity-Ww mold)/Ww mold] x 100

where V is the volume in cc and ww is the weight of water filled in the cavity or mold in grams.

Starting from the same mold and under the same thermoforming conditions, the more formable the material is, the more the percentage difference in volume tends to be 0%, as the volume of the cavity tends to the volume of the mold.

By using a T200 MULTIVAC machine (heating plate above the forming station, heating temperature 190°C, heating time: 2.5 seconds, forming time: 2 seconds) using a mold with dimensions: 135 mm x 180 mm x 50 mm at a depth of 50 mm The material was thermoformed for testing.

The test is particularly useful for comparison purposes because, for a fixed mold and thermoforming conditions, it allows the actual formability of different materials to be compared simply by weighing the corresponding thermoforming containers filled with water.

Membrane properties

Shrinkage, mechanical and optical properties of the films used in the method of the present invention are collected in Table 3 below:

table 3

These properties were measured according to the methods described above.

Film 7 and a commercial comparative thermoformable film (MylarCKP5E) were evaluated for percent free shrinkage and maximum shrinkage tension before and after thermoforming using previously reported test methods and are collected in Table 4 below:

Table 4

Thermoforming was carried out on a T200 MULTIVAC machine equipped with a mould with dimensions of 135 mm x 180 mm x 50 mm under the following operating conditions: heating temperature 180°C, heating time: 1.5 seconds, forming time: 1.5 seconds.

Example 1: Deep Drawing

Film 8 (25 microns) and the commercial comparative film Mylar® OL25 (25 microns) were used with a T200 MULTIVAC machine (heating plate above the forming station, heating temperature 190°C, heating time: 2.5 seconds, forming time: 2 seconds) with dimensions: 135 mm x 180 mm x 50 mm molds are thermoformed at a depth of 50 mm.

For both materials, the draw ratio is 2.3.

Containers according to the invention are of uniform thickness, well-defined and conform closely to the details of the mould, with negligible retraction once removed from the mould.

Film thickness after thermoforming was evaluated on 10 samples of each film and the results were as follows:

table 5

The operator visually evaluated the formability of the film, and judged the film 8 better. In terms of possible "retraction" effect and "pouch clarity", the features evaluated were the depth achieved in the mould and how precisely the shape of the container formed corresponds to the shape of the mould.

As can be seen from the above data in Table 5, the film 8 was formed smoothly with a more uniform distribution (ie, constant thickness) than the commercially available films.

The thickness variation (calculated as a percentage relative to the theoretical mean) of container A according to the invention is about ±4.4% for the bottom and about 0% for the wall, while for the comparative container B it is about ±20% for the bottom, And about ±71% for the wall.

Furthermore, the film 8 conforms better to the shape of the mold, creating a cavity of greater volume, as demonstrated by the following volume test (shrinkage index after thermoforming).

Ten containers (A) made of film 8 as described above and ten containers (B) made of Mylar® OL25 were filled with water up to the flange and weighed. The average weights of filled containers A and B were 905 g and 740 g, respectively.

Considering the mold dimensions of 135 mm x 180 mm x 50 mm, the maximum volume of the mold is 1215 cc, which corresponds to 1215 g of water.

It can be seen that the percentage of the water weight difference between the mould and the formed container, which corresponds to the volume difference ΔV, is -25% for container A according to the invention and -39% for comparative container B.

From these data it can be seen that the films used according to the invention, characterized in that the polyester in the base layer b) has an intrinsic viscosity higher than 0.75 dl/g, have a higher intrinsic viscosity than commercially available polyester Mylar films of comparable thickness Good formability. Advantageously, Container A of the present invention has an increased packaging capacity with a significant improvement in cost and carbon footprint compared to Container B made from a commercial polyester-based film of the same thickness.

Example 2: Deep Draw Thermoforming-Shrinkage Method

deep drawing step

Film 7 (33 microns) and a commercially available comparative film Mylar® from DuPont Teijin Films were made at a depth of 50 mm using a T200MULTIVAC machine equipped with a die measuring 135 mm x 180 mm x 50 mm under the following operating conditions OL25 (24 microns) and Mylar® OL40 (38 microns) were thermoformed to give rectangular containers C, D and E, respectively:

Heating temperature 180°C, heating time: 1.5 seconds, molding time: 1.5 seconds.

The draw ratio is 2.3 for all materials.

Pictures of containers C, D and E are reported in Figure 2.

As can be understood from these pictures, neither the commercial films Mylar® OL25 nor Mylar® OL40 achieved satisfactory pouch clarity when molded: the walls were round, the material was wrinkled, and it did not fully follow the design of the mold.

In contrast, Film 7 had very good clarity under the same conditions: the material remained in tension and conformed significantly to the mold walls, and the volume of the cavity was significantly higher than that of the control.

In conclusion, the formability of the test materials was evaluated visually by the operator, and the formability of Film 7 was judged to be much better than the commercial films Mylar® OL25 and Mylar® OL40.

Packaging and Shrinking Steps

Twenty containers of each type (C, D and E) were loaded with drumsticks, evacuated and hermetically sealed at a temperature of 200°C by using the same film on the bottom as the top web to provide Packages C, D and E .

Twenty additional packages (for each material and for each temperature) were prepared under the same conditions as above, but the sealing temperature was set at 185°C and 220°C, thus providing packages C1, C2, D1, D2, E1 and E2 respectively .

All sealed packages were then passed through a shrink tunnel (CJ61-CRYOVAC, belt speed 4.5 m/min at 180°C) and shrunk.

The shrink wraps (C, C1 and C2) according to the invention are tighter and more attractive, the material conforms better to the product relative to the shrink wraps D, D1, D2 and E, E1, E2 made of commercial films shape.

The absence of wrinkles and the excellent optical properties of the packages (C-C2) according to the invention make these packages more attractive and easy to inspect visually.

Example 3: Cooking Test

Ten packages of each type of package (C, C1, C2, D1, D2 and E, E1, E2) prepared as described under Example 2 were kept in a ventilated conventional oven at 180°C for 30 minutes. The package was then removed from the oven and evaluated by visual inspection for the following characteristics:

- Air tightness and self-venting : prior to cooking, the seal is air tight with no leaks for all packages tested. During cooking, due to the composition of the top sealing layer, packages C-C2 according to the invention open the limited length of the sealing area, allowing the internal pressure of the package to be released (self-venting), but without excessive escape of internal moisture. In contrast, the packages D/E/D1/E1 made of the commercial films Mylar® OL25 and OL40 open the longer part of the seal and thereby lose more baking liquid. Package D2/E2 cannot self-vent (seal too strong).

- Peelability : Assess 1 to 2 minutes after removing the package from the oven. For package C-C2 according to the invention, the top was easily removed and peeled cleanly (no burrs or tears). Packages D, E, D1 and E1 were also easily opened since most of the seals had failed during cooking. Finally, package D2/E2 is more difficult to open.

- Cooked product appearance : The drumsticks of package C-C2 according to the invention were well cooked and seasoned, tender and juicy on the inside, but browned (baked) on the surface. Considering the comparative package D/E/D1/E1 made from the commercial film Mylar, a long part of its seal was opened during cooking and more cooking liquid was lost, the film was browned and the cooked product was more juicy Small. Finally, the drumsticks of package D2/E2 were pale in color and unbaked.

Relevant characteristics and operator observations of the packages tested are summarized in Table 6 below:

Table 6

The same cooking test was repeated at 200°C and 220°C with comparable results in terms of air tightness, self-venting, peelability and cooked product appearance.

Example 4

The sausages were packaged in thermoformed-shrink wraps with the same films used for top and bottom, in particular film 8 was used for the package according to the invention, while the commercial film Mylar® OL25 was used for the comparative package.

Thermoforming of the bottom web was carried out according to the following conditions: T200 MULTIVAC machine at 190°C, 2.5 sec heating time, 2.0 sec forming time, depth 50 mm (mold dimensions: 135 mm x 180 mm x 50 mm).

The sausages were loaded into the cavity and the opening was closed under vacuum by sealing the same corresponding top web (Film 8 or Mylar) at 200°C (sealing time: 2 seconds). Shrink wrap in air at 180°C in shrink tunnel CRYOVACCJ-61 with a belt speed of 6 m/min.

Photographs of these packages after vacuum sealing and after shrinking are reported in Figures 4 and 5.

As can be appreciated from Figures 4A and 4B, the packaging 4A according to the invention is tighter and has no or very few wrinkles, even before shrinking, because the film conforms better to the product despite the larger volume of the thermoforming cavity contour. In fact, as demonstrated above - see Example 1 , the film used in the thermoforming packaging method of the present invention is more formable than the comparative film Mylar, providing a larger thermoforming cavity.

The difference in appearance is even more pronounced when considering the shrink wraps of Figures 5A and 5B: the shrink film of package 5A according to the invention remained taut and wrinkled, while the film of comparative package 5B did not conform well and remained wrinkled.

The absence of air pockets within Package 5A is of particular interest as it extends the shelf life of the product as it avoids the presence of residual oxygen which can lead to oxidative degradation and liquid (potential medium for bacterial growth) accumulation. Furthermore, the packaging according to the invention is more attractive than the comparative packaging.

In conclusion, the thermoformed package according to the invention is characterized by a deep-drawn container which conforms to the mould very well, resulting in an increased packaging capacity for the same thickness and the same amount of material compared to commercial polyester-based materials.

The packaging of the present invention in a shrinkable form is more attractive, with a tight film without wrinkles. Furthermore, the package of the present invention is suitable for reheating and packaged cooking food in microwave ovens, conventional and convection ovens, showing good air tightness, clean peelability, self-venting and very good optical properties.

Claims (31)

1. a thermoformed food packaging method for the manufacture of a thermoformed package that can be baked by a dual process, comprising: - to provide a thermoformable bibakeable biaxially oriented polyester film as the bottom web, - forming the bottom web so as to provide at least a cavity with openings; - placing food product in said cavity through said opening; - at the opening, by air-tight sealing the bottom web itself or by providing a dual-bakeable top web and hermetically sealing the dual-bakeable top web around the opening sealing to the bottom web to close the cavity; and - cut out said sealed package, characterized in that the film of the bottom web comprises: outer heat-sealable polyester layer a), An inner polyester base layer b) comprising a polyester having an intrinsic viscosity (IV), measured according to ASTM D4603-03, of higher than 0.75 dl/g, outer polyester layer c), and i) the bottom web is formed with a draw ratio higher than 1.26, or ii) the film of the bottom web is heat shrinkable and the sealed package is eventually heat shrunk, Among them, polyester film exhibits significant shrinkage properties after thermoforming, thus allowing tight shrinkage around the product and improved appearance of the package without wrinkles or void air after gentle heating in the air shrink tunnel. 2. The packaging method of claim 1 wherein i) the bottom web is formed at a draw ratio higher than 1.26, and ii) the film of the bottom web is heat shrinkable, and the sealed package Eventually heat shrunk. 3. The packaging method of claim 1 or 2, wherein the film of the bottom web consists of an outer heat sealable polyester layer a), an inner polyester base layer b) and an outer polyester layer c), the inner polyester layer The base layer b) comprises a polyester having an intrinsic viscosity (IV), measured according to ASTM D4603-03, of above 0.75 dl/g. 4. The packaging method of claim 1 or 2, wherein the step of closing the cavity at the opening is performed under vacuum. 5. The packaging method of claim 1 or 2, wherein the total thickness of the film prior to thermoforming is less than 50 microns. 6. The packaging method of claim 1 or 2, wherein the thermoformed food packaging method is a deep draw packaging method, wherein the draw ratio is higher than 2.0. 7. The packaging method of claim 1 or 2, wherein the method is a thermoforming-shrink wrapping method, wherein the film of the bottom web has at least 3% in at least one of the LD or TD directions prior to thermoforming Percent free shrinkage, measured according to the following test methods: - Cut a 12 cm x 12 cm square sample from the membrane; - On the surface of each sample, draw with a pencil a central square of 10 cm x 10 cm; - place the sample in a laboratory oven at 180°C for 5 minutes in air without restriction; - measure the dimensional change in both LD and TD of the delineated squares of each sample; - For each of the LD and TD directions, calculate the percent free shrinkage with the following formula [(Lo -Lf)/Lo] x 100 where Lo is the initial length of the film sample before testing, in mm, and Lf is the length of the film sample after shrinking, in mm. 8. The packaging method of claim 1 or 2, wherein the method is a thermoforming-shrink packaging method, wherein the film of the bottom web has a total free shrinkage percentage of at least 5% prior to thermoforming, the total free shrinkage percentage is the sum of the % free shrinkage on the LD and TD of the film sample as measured in the packaging method described in claim 7. 9. The packaging method of claim 1 or 2, wherein the film of the bottom web is further characterized by - a tensile strength of at least 1500 Kg/cm ² in at least one of the LD or TD directions, and/or - an elongation at break of at least 100% in at least one of the LD or TD directions, and/or - Modulus of elasticity in at least one of the LD or TD directions of at least 20,000 Kg/cm ² , all of these properties measured according to ASTM D882 at 23°C. 10. The packaging method of claim 1 or 2, wherein the biaxially oriented film of the bottom web is oriented in both the LD and TD directions. 11. The packaging method of claim 1 or 2, wherein the polyester of the base layer b) of the film of the bottom web has an intrinsic viscosity (IV) of at least 0.8 dl/g. 12. The packaging method of claim 1 or 2, wherein the film of the bottom web comprises - a heat sealable layer a) comprising about 25 to 70% by weight of at least a first amorphous polyester having a melting temperature not higher than the melting temperature of the polyester of said base layer b), 10 to 20% by weight of at least thermoplastic resin selected from polyamide, polystyrene, polyethylene, ionomer, ethylene/unsaturated carboxylic acid copolymer, ethylene/unsaturated ester copolymer, ethylene/propylene copolymers, maleic anhydride modified polyethylene and ethylene/cyclic olefin copolymers, and 20 to 60% by weight of at least other polyesters characterized by an intrinsic viscosity of at least 0.75 dl/g or higher, and/or by a glass transition temperature Tg of not higher than 80°C and/or by a melting point higher than 240°C, as measured according to ASTM D3418; and/or - an inner polyester base layer b) comprising a mixture of at least 50% polyester resin with an intrinsic viscosity higher than 0.75 dl/g and at most 50% amorphous polyester; and/or - an outer polyester layer c) comprising a polyester characterized by an intrinsic viscosity of at least 0.75 dl/g or higher, and/or by a glass transition temperature Tg of not higher than 80°C and/or a melting point Above 240°C, it is measured according to ASTM D3418. 13. The packaging method of claim 1 or 2, wherein the film of the bottom web consists of - a heat sealable layer a) comprising about 25 to 70% by weight of at least a first amorphous polyester having a melting temperature not higher than the melting temperature of the polyester of said base layer b), 10 to 20% by weight of at least a thermoplastic resin selected from the group consisting of polyamide, polystyrene, polyethylene, ionomer, ethylene/unsaturated carboxylic acid copolymer, ethylene/unsaturated ester copolymer, ethylene/propylene Copolymers, maleic anhydride modified polyethylene and ethylene/cyclic olefin copolymers, and 20 to 60% by weight of at least other polyesters characterized by an intrinsic viscosity of at least 0.75 dl/g or higher, and/or by a glass transition temperature Tg of not higher than 80°C and/or by a melting point higher than 240°C, as measured according to ASTM D3418; and - an inner polyester base layer b) comprising a mixture of at least 50% polyester resin with an intrinsic viscosity higher than 0.75 dl/g and at most 50% amorphous polyester; and - an outer polyester layer c) comprising a polyester characterized by an intrinsic viscosity of at least 0.75 dl/g or higher, and/or by a glass transition temperature Tg of not higher than 80°C and/or a melting point Above 240°C, it is measured according to ASTM D3418. 14. The packaging method of claim 1 or 2, wherein the film of the bottom web consists of - a heat sealable layer a) consisting of: about 40 to 70% by weight of at least a first amorphous polyester having a melting temperature not higher than the melting temperature of the polyester of said base layer b), 10 to 20% by weight of at least a thermoplastic resin selected from the group consisting of ethylene/unsaturated carboxylic acid copolymers, ethylene/unsaturated ester copolymers and maleic anhydride modified polyethylene, and 20 to 50% by weight of at least other polyesters characterized by an intrinsic viscosity of at least 0.75 dl/g or higher, and/or by a glass transition temperature Tg of not higher than 80°C and/or by a melting point higher than 240°C; and - an inner polyester base layer b) consisting of a mixture of at least 55% polyester resin with an intrinsic viscosity higher than 0.75 dl/g and at most 45% amorphous polyester; and - an outer polyester layer c) comprising at least 95% of the same polyester as said base layer b), characterized by an intrinsic viscosity of at least 0.75 dl/g. 15. The packaging method of claim 1 or 2, wherein, in the film of the bottom web, the base layer b) comprises the same amorphous polyester and/or the same amorphous polyester of the outer heat sealable polyester layer a) . The polyester of the outer polyester layer c) is the same polyester of the base layer b), the intrinsic viscosity of which is higher than 0.75 dl/g. 16. The packaging method of claim 1 or 2, wherein the film of the bottom web is a coextruded film. 17. A dual bakeable thermoformable flexible container manufactured by thermoforming a film of the bottom web of any preceding claim, the container comprising a thermoformed cavity and an opening, wherein The depth of the thermoformed cavity is greater than 1 cm or the thermoformed container is heat shrinkable. 18. The flexible container of claim 17, wherein the depth of the thermoformed cavity is greater than 1 cm, and the thermoformed container is heat shrinkable. 19. The flexible container of claim 17 or 18, wherein the stretch ratio of the thermoformed container is higher than 1.26. 20. The flexible container of any of claims 17 to 18, wherein the thermoformed cavity has a depth greater than 2 cm. 21. The flexible container of any one of claims 17 to 18, wherein the thermoformed film has a total free shrinkage percentage after thermoforming of at least 40%, measured according to the following test method: - Cut a 7 cm x 7 cm square sample from the bottom of the thermoformed film; - On the surface of each sample, draw with a pencil a central square of 5 cm x 5 cm; - place the sample in a laboratory oven at 180°C for 5 minutes in air without restriction; - measure the dimensional change of the delineated squares of each sample in both the LD and TD directions; - For each of the LD and TD directions, calculate the percent free shrinkage with the following formula [(Lo -Lf)/Lo] x 100 where Lo is the initial length of the film sample before testing, in mm, and Lf is the length of the film sample after shrinking, in mm. 22. The flexible container of any one of claims 17 to 18, wherein the container further comprises a flange surrounding the opening, the flange adapted to be sealed to a dual bakeable top web. 23. An air-tight thermoforming package that can be double-baked, comprising The dual bakeable thermoformable flexible container of any one of claims 17 to 22, comprising a thermoformed cavity and an opening, food placed in said cavity, The opening is hermetically closed by a flexible container that is self-sealing at the opening or by a dual bakeable top web sealed around the opening to the container. 24. The package of claim 23 which is a vacuum package. 25. The package of claim 23 or 24, wherein at least the flexible container is heat shrunk. 26. The package of any of claims 23 to 24, wherein a top web is present and the top web is heat shrunk. 27. The package of any of claims 23 to 24, wherein the flexible container and the top web are made of the same film. 28. The package of any of claims 23 to 24, wherein the top web is also thermoformed. 29. The package of any one of claims 23 to 24, wherein the food product is selected from fish, meat, processed meat, poultry, pork, lamb, baked goods, seafood, stabilized vegetables, or ready meals. 30. A method for cooking food comprising - providing the dual bakeable thermoformable package of any one of claims 23 to 24 which hermetically closes the food product, and - Cook the packaged food in the package in a microwave or in a conventional oven. 31. The method of claim 30, wherein cooking the packaged food product is performed in a conventional oven at a temperature above 205°C and/or at most 220°C.

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